Slow Roasted Baked Onions

This baked onion side dish is easy to make for a simple, flavorful holiday side. Make this recipe to serve with your holiday ham, turkey, or beef roast.

This recipe is worth you taking a look at. Really. It’s not a typical holiday side dish like traditional French’s green bean casserole or roasted potatoes, but I bet you’ll love it just as much. The onions caramelize roasting in a bath of red wine vinegar, brown sugar and spices.

The result is a tender vegetable that’s soft and creamy on the inside and caramelized on the outside. The flavor is mellow and sweet, and it takes on the flavor of the marinade, making a memorable side on your holiday table.

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.

Baked Onion – Choosing the Right Variety

1. Best Onions for Roasting / Baking

Because this is a side dish recipe, the best option is to use an extra large variety of onion. You’ll be slicing them in half and leaving the skins on while they bake, so I recommend using a large, sweet variety like Vidalia or yellow. You could even use red onion, which also tastes fantastic caramelized!

2. Choosing a variety based on the protein you’re serving.

• Poultry– If you’ll be serving the roasted onions with a roast turkey, I think yellow is your best option.
  
• Pork– The best option to serve with a holiday ham is definitely Vidalias. Their sweetness pairs perfectly with glazed ham, especially if you’ll be using a slightly spicy glaze like chipotle orange.
  
• Beef or Lamb– For boneless prime rib, lamb roast, or braised beef brisket, any type of onion works well. This is where making baked roasted red onions might be a great choice.

Video: Making Marinated Roasted Onions

The recipe is pretty simple and aside from the marinating, it’s really quick and easy to make. Watch the video in the recipe card to see the process from start to finish.

Planning Ahead

This roasted onions recipe is one you need to plan ahead for, as the onions need to sit and marinate overnight before roasting. While you’re at it, these Herb Roasted Potatoes could easily be made at the same time!

NOTE:
I’ve roasted onions without marinating, and they’re okay. But I feel the overnight soak really makes a difference. If you’re crunched for time and need to skip the overnight soak, at least let them marinate for an hour if you’re able to.

This is a rich and flavorful side dish, and it really does go well with nearly every protein you can think of. For a nice garnish and punch of flavor, I occasionally add fresh chopped rosemary during the last 5 minutes of baking time.

This post, first published on Kevin Is Cooking November 2017, was last updated with new content on Sept. 11, 2021.

Slow Roasted Baked Onions + Video

This baked onion side dish is easy to make for a holiday side dish. Make this recipe to serve with your holiday ham, turkey, or beef roast.

4.84 from 31 votes

Print Pin Rate

Course: side dishes

Cuisine: Melting Pot

Prep Time: 5 minutes

Cook Time: 1 hour

Total Time: 1 hour 5 minutes

Servings: 8

Calories: 90kcal

Author: Kevin Is Cooking

Ingredients

Marinade

• 1 cup water
• 1 cup red wine vinegar
• 2 tbsp brown sugar
• 1 tsp fresh rosemary chopped
• 1/2 tsp salt
• 1/4 tsp black pepper
• 1 pinch red pepper flakes optional
• 4 large onions (See Note 1)

Roasting

• 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 8×8″ 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 cut 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 uncovered 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

1. White, yellow, or red onion may be used. Trim ends off onions, slice in half horizontally, keeping the skin on to hold shape and protect the outside as it roasts. Just peel and discard the skins before serving.

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.

Nutrition

Serving: 1g | Calories: 90kcal | Carbohydrates: 8g | Protein: 1g | Fat: 6g | Saturated Fat: 4g | Cholesterol: 15mg | Sodium: 203mg | Potassium: 92mg | Fiber: 1g | Sugar: 5g | Vitamin A: 177IU | Vitamin C: 4mg | Calcium: 19mg | Iron: 1mg

Have you made this recipe? Let me know on InstagramTag @KevinIsCooking and hashtag me #keviniscooking!