These Marinated Slow Roasted Onions are a side dish that are worth you taking a look at. Really. Not your typical side dish like a green bean casserole or a baked potato, these onions caramelize roasting in a bath of red wine vinegar, brown sugar and spices.
The result is a soft and creamy on the inside and caramelized on the outside onion that mellows in flavor and takes on the marinade to make a memorable side on the holiday table.
Roasted onions you say? Why yes, these Marinated Slow Roasted Onions are incredibly delicious and so easy to make and the aroma will get your mouth watering. I wanted to share with you a quick and tasty side dish today with all the upcoming holidays.
These make it to our table more times than I can count because they don’t need a holiday reason to sing and are perfect with grilled meats when no holiday is the reason.
Trimmed onions get sliced in half horizontally, keeping the skin on to hold shape and protect the outside as it later roasts. Then marinade overnight, dab with some butter, chopped rosemary and slow roast in the marinade. Heavenly!
This one you need to plan ahead for as the onions marinate overnight before roasting. While you’re at it these Herb Roasted Poupon Potatoes could easily be made at the same time!
I’ve made them without marinating and feel the overnight soak really makes this rich and flavorful. I occasionally add fresh chopped rosemary at the last 5 minutes of roasting for an added punch of flavor. Enjoy!
This recipe first appeared on Kevin Is Cooking November 2017 and has been updated with a new video.
Marinated Slow Roasted Onions
Ingredients
- Marinade:
- 1 cup water
- 1 cup red wine vinegar
- 2 tbsp brown sugar
- 1 tsp fresh rosemary chopped
- 1/2 tsp kosher salt
- 1/4 tsp black pepper
- pinch red pepper flakes optional
- 4 large white or yellow onions (See Note 1)
- 4 tbsp butter
- 1 tsp fresh rosemary chopped
Instructions
- Blend marinade ingredients in small bowl and pour into a baking dish that will hold all 8 onion halves. I use 8x8" baking pan or round 12" baking stone (pictured) depending on size of onion.
- Trim the end of onions and cut horizontal (leaving skin on) and place wide side down in marinade. Marinate overnight covered in refrigerator.
- Preheat oven to 400°F. Flip the onions over in the marinade, and lay on the flat bottom of each side. Top each onion with 1/2 tablespoon of butter and remaining teaspoon of rosemary.
- Roast in oven for 1 hour or until golden brown, basting once or twice during roasting. Remove from heat, spoon reduced sauce over and sprinkle with parsley or more fresh chopped rosemary. Remove outer skins before eating and serve.
Notes
Question:
Can the sugar be omitted and still have good flavor?
I couldn’t truthfully answer that as I have never tried it that way Natalie. If you do try it that way I’d love to know how it turns out.
2(ish) questions: 1. I have to prepare these to a point where they only need about 30 minutes of cooking because our turkey takes up the whole oven. (It’s 20+ pounds and has to be perfectly centered or the rack collapses.) Once the turkey comes out, all of the sides–and ham–go in. I know it’s not ideal, but can I cook these most of the way? 2. I want to toss in a bunch of garlic cloves. Should I marinate them as well? (Why not?) Will they cook okay or might they burn on the outside and remain raw inside?… Read more »
I think that would be fine pre-cooked and then finished off later Jill. As for the garlic, that sounds like a great idea and I would roast them with the onions from the start.
Thanks, Kevin. It came out great. I doubled the recipe and used smaller onions to reduce cooking time. I used less vinegar as someone suggested. (My husband’s family prefers plain, boiled onions. Every year I try to make some changes–sometimes I go too far.) The cooking method worked well. Creamy inside, indeed! I tossed in 2 1/2 bulbs of peeled garlic. They oddly turned purply blue, but they tasted fine. My husband ate the leftovers 4-5 hours after Thanksgiving dinner–literally sat down to a small bowl of the onions and garlic. I asked him if he liked it. He said… Read more »
So happy to hear this Jill and at least he tried them, right? Thanks for taking the time to come back and let me know. 🙂
Have you made with sweet onions? Does it have a good flavor, or is it less appealing using this method?
I have and loved that as well Lise. Sweeter than savory, but quite tasty. 🙂
Have you ever roasted chicken, carrots or potatoes on top of the onions while they cook?
No, but that sounds like Sunday’s dinner! Thanks Mel. 🙂
Never cooked anything with onions as the main ingredients except fried onion rings. These onions seem so right for my flu right now 😅 – Natalie
Hope you’re feeling better and you enjoyed these Natalie!
Love roasted onions and your marinated ones sound wonderful…can’t wait to give them a try.
I rotate these year long, but they are always a hit around the holidays, too. Thanks Karen!
Made these tonight and they were a huge hit. We loved them! A new go to sude dish. Great flavors!
Excellent, love to read comments like this Danielle. It’s always a big hit around our place during the holidays for company, but we eat them year round. Thanks!
These onions look divine! The perfect side to so many mains!!
I have made many of your recipes and we (family) just love them. Can’t wait to make this one! Looks amazing
Thanks so much Kristine, really appreciate you taking the time to come back and let me know!
I’m def making these. This is my most favorite idea ever. These sound absolutely divine. I absolutely cannot wait to make these. What a great combo with the brown sugar and the red wine vinegar. Love, love love this Kevin!!
You’re going to love these Danielle. The insides get creamy soft and the slightly charred exterior is slightly tart and caramelized. Such great flavors! I’ve made with red onions too. So good. 🙂
Followed recipe exactly as printed. The onions even looked exactly like the photo. However, the cooked onions tasted too vinegary. Maybe less red wine vinegar or more water or more brown sugar to tame the tartness? I was thinking of trying it again with 1.5 cups of chicken broth, 1/4 cup water and only 1/4 cup of red wine vinegar and a bit of Worcestershire sauce for some zing.
The tartness of the vinegar with the mellow, rich flavor of the slow roasted onions are what I love, but feel free to adjust to suit your tastes. Let me know how your next batch comes out, like your idea. Cheers!
I am a newbie in the kitchen. Probably a stupid question, when u say trim ends, do you mean to cut the ends so that they have flat ends and can sit?
No worries ET, yes, trim the ends.
This recipe turned out great for me. Made these twice now for dinner parties, and my guests loved them. Not understanding the below commenter (Simon), unless he varied from the recipe. Maybe he didn’t keep the skins on?
I think that might have been the issue, but not sure about the other part. Thanks for stopping by and letting me know Kenny. These always come out great, we love the flavor and you just need to be careful not to over cook them, right? Cheers! 🙂
This is a shockingly bad recipe. I followed it exactly. The onions don’t stay together, they go straight to black, and you end up eating sour pickled onions. Shudder. Will never follow a Kevin recipe again.
Almost all the comments here merely talk about how they LOOK great. Has anyone actually made them like me? Doubt it.
Sorry to read that was your experience Simon. I hope you read the recipe correctly and kept the skin on the onions until AFTER cooking them, it is crucial and keeps them from falling apart. Other than that, I and others make this often and have never had BLACK onions. As you can see here your comment was approved because I have no issue with people having a problem, leaving a comment and hopefully I find a solution so others can read and learn too. If you read the above comment, he (Kenny) had no issue and makes them with… Read more »
Fantastic! I added a bit of bread and butter pickle brine, Worchesteier sauce, red pepper flakes, clove and a pinch of mustard seed to my marinade, it was amazing. What was exquisite was the left over onions that I made into breakfast by putting them into grease muffin pan and pouring a eggs over them. I then topped them with some gruyere half way through baking. I topped my with loxs but not all my guest were salmon fans. Oh well their loss more for me.
Love your breakfast creation Brent! Thanks for coming back to let me know. 🙂
[…] Perfectly caramelized with a soft and creamy middle.Marinated Slow Roasted Onions […]
These are delicious! Thank you so much. How long do they keep?
Hahaha I wrote before reading your response. Sorry! Don’t know how I missed it. I am eating them right now with sous vide chicken breast in a simple tomato sauce, because that’s what I was having anyway. Poured the marinade into the sauce and it is amazing. Thinking of separating the outer two layers and stuffing them with shark tartar (with avocado, fennel, jalapeño and green apple) as appetizers.
Now that sounds like one amazing meal. Thanks for letting me know Alexander!
Looks delicious! Can they be made ahead, and if so, how long do they last? Thank you very much!
In my opinion marinate and keep them covered and refrigerated, but don’t roast them if doing ahead. Unless it’s an hour or so. I feel the texture wouldn’t be the same. I have had leftovers and they are delicious, but fresh from the oven is best. Let me know what you think Alexander. Cheers!
What type of onions should I use?
Hi there Peter! I use either white or yellow onions for this one. I have actually used red as well, but used white here in these photographs. All work exceptionally, but I lean more to the white personally. Hope this helps!
[…] Marinated Slow Roasted Onions | Kevin is Cooking […]
I am definitely going to save this recipe to make over the weekend. I have a beautiful roast they would be perfect to serve with!
Stunning pictures too
Thanks so much Brynn! I hope you’ll enjoy them. 🙂
These are stunning! Love the pictures! They are making me drool!
Thanks Zerrin, they actually taste as good as they look, too! Have a wonderful weekend. 🙂
What a lovely idea, these sound so delicious. A great recipe for autumn!
Thanks Caroline, they really are pretty amazing as a side dish. Cheers!
You are totally speaking my language with these onions Kevin! I think I could eat the whole entire pan! No shame. Perfect with a nice juicy steak! Happy weekend!
You’re going to love the aroma and they taste even better! Thanks Mary Ann.
Kevin! I can’t even with this! I want to swim in that pan! I am a huge fan of onions. A huge fan of anything roasted. And a huge fan of all that you produce. Oh. My. God. That’s all.
Thanks Annie, you are one of my reader and fellow food blogger friends that always puts a smile on my face! 🙂
Hey Kevin! We eat tons of onions and these will be on the table soon! These would be lovely as a side with Nagi’s leg of lamb she posted today! Can I include this in the “holiday” fare?
By all means include! Thanks Dorothy 🙂
They look great. Can’t wait to try. One question, your pictures show a pat of what looks like butter on each onion half but it isn’t in the recipe. I do think everything (at least most things) are better with butter so I thought I would ask. Should butter be in the recipe?
I couldn’t agree more David! Updated to reflect, thanks for the eagle eye my friend! Hope you enjoy these.
Oh my! These are beautiful!! I can think of so many upcoming get togethers where these onions will impress…and vanish, but I also see these in my weekly menus, the overnight marinade sounds incredible and easy. Rosemary is one of my absolute favorite herbs, too. Two thumbs up!
Thanks so much Sally, they’re a house favorite too. Just make sure, due to different sizes of onions, that they are tender as times may vary. 🙂
What a delicious idea! I’ve never done marinated onions on the stovetop like this, but we love brushing thick-cut onions with herbs and olive oil and then tossing them on the grill. This sounds like the winter version of that one…and I definitely need this to happen soon! Love it!
Awesome to hear, these are a fantastic side whether it’s a holiday dinner or not Dave. That vinegar mellows as do the onions slow roasting like that, but the flavor combo is wonderful.
I’ve made roasted onions before, but these look SO much better! I can tell you one thing’s for sure….these are in my future. Can’t wait to try and love how all the onion layers opened up a bit. Onions are complex like that, lots of layers to their personality, lol 😉 And you know I’m all over this recipe ’cause of the vinegar. The rosemary at the end is a nice touch and pop of colour too. Pinning!
Thanks Dawn, these get almost creamy inside, but hold their shape. I love the roasted edges and the surprising flavor from the vinegar is awesome. 🙂