Slow Roasted Red Onions

5 from 4 votes

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My recipe for roasted red onions is simple to make but delivers major results. Soy sauce, brown sugar, red wine vinegar, and spices infuse the onions as they caramelize to create a flavor profile that is out of this world.

Roasted Red Onions on a white plate

Roasted red onions are a quick and easy side dish that will take any meal to the next level. They deliver a deep earthy sweetness and a divinely creamy texture. The soy sauce and red wine vinegar in the marinade add the perfect dash of tanginess, while the caramelization process turns the whole dish into a mouthwatering masterpiece.

This recipe is so flavorful and versatile, it might just end up on your dinner table multiple times per week! These onions take virtually no time to prepare and make everything taste phenomenal. I especially enjoy pairing this dish with dark meat such as beef or lamb. I recommend making a batch alongside my Greek Grilled Lamb Loin Chops, Southwest Flap Steak, or Reverse Sear Cowboy Steak

Make this roasted red onions recipe for family barbecues and holiday potlucks as well! Serve them alongside your next Thanksgiving turkey or Christmas ham. And don’t forget to round out your meal with Roasted Mashed Potatoes or Roasted Brussel Sprouts.

closeup of Roasted Red Onions


  • Red Onions – The main ingredient for this recipe! They are a bit spicy, a bit sweet, and add a lovely dash of color to the dish. It is perfectly okay to use yellow, white, or Vidalia if you prefer — just understand that the flavor profile will be a bit different.
  • Olive Oil – I love this flavor this adds, but avocado oil is another great choice.
  • Kosher Salt – Accentuates the natural flavor of the other ingredients without making everything taste overly salty. Feel free to substitute sea salt or Himalayan pink salt.
  • Black Pepper – Freshly ground black pepper adds the perfect amount of subtle heat. 
  • Red Wine Vinegar – This ingredient adds a tangy brightness to the marinade. 
  • Brown Sugar – The sweetness of brown sugar balances out the sharper flavors of the soy sauce and vinegar while enhancing the caramelizing of the onions. 
  • Soy Sauce – Delivers deep umami and salty deliciousness to the marinade and the entire dish.


  1. Preheat Oven. Preheat the oven to 500 degrees F and place the rack in the lower third of your oven. 
  2. Arrange Onions. Choose a 9×12” baking pan that is big enough to hold all of your onion slices. Arrange sliced onions in the pan as evenly as possible. 
  3. Make Marinade. Use a small bowl to whisk together the water, soy sauce, red wine vinegar, and brown sugar for your marinade. 
  4. Season Onions. Pour the marinade all over your sliced onions and drizzle with olive oil, kosher salt, and black pepper. If desired, cover your dish with plastic and allow the onions to marinate in the refrigerator overnight for an even deeper flavor. 
  5. Roast. Place the baking pan in the oven and allow your onions to roast for about 30 minutes. You want the liquid in the pan to become syrupy and the onions to be decently charred. 
sideview of Roasted Red Onions

How Do You Store Leftover Roasted Red Onions?

If you end up with leftovers, storage is a breeze. You can simply store them in an airtight container in the refrigerator for 3-4 days. I wouldn’t recommend freezing them, though.

Reheat in the oven or in a skillet over medium heat until warmed through. In a pinch, you can also microwave individual servings.

What Do Roasted Red Onions Taste Like?

Something magical happens during the roasting process turning crisp, spicy onions into a sweet and creamy side dish. The sharpness of raw onion gets replaced with a mellow yet deeply complex flavor. The result has a bit of umami, tanginess, sweetness, spice and a whole lot of gusto. The charring and caramelization add just the right amount of smokiness to turn the whole dish into a flavor explosion. 

closeup of Roasted Red Onions

How Can I Speed Up Caramelizing Onions?

This recipe already has the secret ingredients to faster caramelization. The high heat of the oven combined with the sugar content of the marinade will expedite the process as much as possible. 

several Roasted Red Onions on a platter
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Slow Roasted Red Onions

5 from 4 votes
These roasted red onions are marinated and charred to perfection, creating an irresistible sweet flavor and creamy texture.
Servings: 4
Prep: 10 minutes
Cook: 30 minutes
Total: 40 minutes




  • Place a rack in lower third of oven and preheat to 500°F.
  • Arrange sliced onions into 9×12″ roasting pan that will hold all onion slices. Blend marinade ingredients in small bowl and pour over onion slices (See Note 1).
  • Drizzle the onions with olive oil, season with salt and pepper. Roast for 30 minutes or until wedges are well charred and liquid has become syrupy.


  1. Cover with plastic wrap and refrigerate overnight for a deeper flavor, optional.


Calories: 136kcal | Carbohydrates: 16g | Protein: 2g | Fat: 7g | Saturated Fat: 1g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 5g | Sodium: 434mg | Potassium: 225mg | Fiber: 2g | Sugar: 9g | Vitamin A: 3IU | Vitamin C: 10mg | Calcium: 38mg | Iron: 1mg

The information shown is an estimate provided by an online nutrition calculator. It should not be considered a substitute for a professional nutritionist’s advice.

Course: side dishes
Cuisine: American
Have You Made This Recipe? Let Me Know on InstagramTag @keviniscooking or tag me #keviniscooking!
ready to serve Roasted Red Onions


Whether in the kitchen or on the grill, you’ll find me cooking American favorites with a love for BBQ, Mexican and Tex Mex. I’m passionate about making tasty food because life’s too short to be bland!

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  1. 5 stars
    Made this last night as a side with air fryer chicken breasts. It was delicious! The flavor complimented the chicken very nicely. Will definitely be making this again. Can’t wait to try it with steaks . BTW, make sure your oven/stove fan is on when you open the oven door– at 500 degrees it might smoke a bit.

  2. 5 stars
    The perfect Christmas Eve side dish for the filet mignon! Making it this weekend too as I just bought a bag of red onions. You have such wonderful recipes and they are always fabulous! TY

  3. 5 stars
    Hey Chef. I’m making this with my Coffee Rubbed Venison Loin for my Dunner Party Saturday. Teamed up with Mashed Sweet PotAtoes with Pecans and a Cherry Cranberry Relish. 

  4. I got a huge bag of shallots at our end of season farmer’s market. I think I will try this recipe, subbing shallots for onions!

      1. 5 stars
        Hi Kevin…just to let you know the shallots worked great. After peeling I cut each shallot in half lengthwise. Otherwise everything the same as your recipe. I did marinate them overnight. What a great recipe!

  5. This looks wild, I am going out today for the red onions can’t wait! This is all about what makes me happy! Thanks