Make ahead marinated red onions are simple to make, and look elegant when served on a fancy platter. The secret ingredient is time, so make sure to allow enough time for the them to marinate overnight.
Looking for other tasty side dishes? You'll enjoy these recipes for roasted sweet potatoes and roasted acorn squash.
Ingredients
Curious what ingredients you need to make these marinated red onions? Here's the most important ones!
- Red Onions: Choose red onions with smooth, undamaged skin. You'll cook the onions with their skins on to help them hold their shape, but remove them before serving.
- Rosemary: Use fresh rosemary if possible, but dried will also work.
- Vinegars: We like to use a combination of sherry vinegar and white balsamic vinegar for a richer flavor.
See recipe card for full information on ingredients and quantities.
Variations
- Need to substitute an ingredient in the marinade? The basic ingredients are water, vinegar, sweetener, and spices.
- Looking for a sugar substitute? Try honey, maple syrup, or rice malt syrup.
- Don't have fresh rosemary? Switch out with another earthy spice like thyme or oregano.
How to Make
Find all the ingredients.
- Use a sharp knife to cut off both ends of each red onion then slice the onion in half. Keep the outer skin on, as it helps them keep their shape. Place them with the largest cut side down in a large baking pan with sides.
- Make the marinade by placing all the ingredients in a bowl. Whisk until well combined.
3. Pour the marinade on top. If you want, sprinkle more fresh rosemary over the cut ends of the red onion. Cover with foil and refrigerate for at least 12 hours.
4. Cook uncovered at 400 F for 30 minutes. Flip each onion over and put a pat of butter on top. Sprinkle more fresh rosemary and a few grinds of black pepper on top. Put back in the oven and bake for 15 minutes more.
5. Take them out and baste them with the marinade using a large spoon. Put back in the oven for another 15 minutes of cooking, baste again, then repeat this process once more.
6. Before serving, remove the tough outer skin. Serve hot on a fancy platter with hot the marinade on the side. Your guests then can spoon more delicious marinade over this side dish to intensify the flavor.
This tasty marinade comes together super fast, and the prep work is quick. Really, what's not to like? Experience something new, and give it a try this week.
Recipe FAQs
Red onions are the highest in antioxidant compounds. Fermented vegetables have probiotics, which helps maintain a healthy gut. They have anti-inflamatory properties due to the flavonoid quercetin. They are high in fiber, folic acid, and vitamin B.
Use a sharp knife. This will give you a cleaner cut so it will cause less damage to the cell wall which will produce less chemicals in the air. Chill the onion in the fridge or briefly in the freezer before slicing. It will retard the release of the sulfuric compounds. Run a vent hood and slice near it. It will take the fumes away from your eyes and bring them outside.
For a serving size of half an onion, there is 86 calories and 13.3g carbs. This recipe is also low in fat and cholesterol. For more nutritional information, scroll past the recipe card.
Serve
These marinated red onions make an impressive side dish for almost any meal. Try serving them with a bowl of creamy wild rice soup or a plate of hearty Salisbury steak. They would also make a great side for steak and ale pie or this meat and potato pie.
If you're looking for other roasted vegetable side dishes, make sure to try our recipes for roasted cabbage wedges and roasted kernel corn.
Expert Tips
- Make this the night before to give time for them to marinade for maximum flavor.
- Keep the onion skins on while baking to help keep their shape. Just remove them before eating.
- The marinade makes this vegetable more flavorful and easier to digest.
- For best flavor, marinate and roast them with the flat side down in the marinade, and then turn them over half way through.
- Tempted to skip the basting? This is an important part of increasing the flavor of the dish.
- Don't throw the marinade out; keep it for guests to spoon over their serving.
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Recipe
Make Ahead Marinated Red Onions
Ingredients
For the Marinade
- 1 cup water
- ½ cup sherry vinegar
- ½ cup white balsamic vinegar
- 2 tablespoons light brown sugar, packed
- 1 heaping teaspoon fresh rosemary, chopped
- ½ teaspoon salt
- ⅛ teaspoon black pepper
For the Roasted Onions
- 4 large red onions
- 2 tablespoons salted butter
- 1 teaspoon fresh rosemary, chopped
- a few grinds of black pepper
Instructions
- Cut the ends off the red onions, then halve them. Keep the skins on, as it helps them keep their shape. Place them flat side down in a baking pan with sides.
- Whisk together the water, vinegars, brown sugar, and spices, and then pour over the onions. Cover with foil and allow to marinate for a minimum of 12 hours.
- Cook uncovered at 400 F for 30 minutes. Flip each onion over, put a pat of butter on top of each onion, sprinkle the rosemary and a few grinds of black pepper on top.
- Cook for 15 minutes more, then take out the pan and baste them with the marinade. Repeat this step two more times.
- Remove the tough outer skins, then serve warm on a pretty platter. Pour any leftover marinade from the baking pan into a small bowl and serve with this dish.
Notes
- Make this the night before to give time for them to marinade for maximum flavor - 12 hours is best for maximum flavor.
- The onion skins should be kept on while baking to help keep their shape. Remove before eating.
- Start by marinating and roasting them with the flat side down in the marinade then turn them over half way through for the best flavor.
- Don't skip the basting part. This important part increases the flavor of the dish.
- Keep the marinade for guests to spoon over their serving.
Nutrition
Serving sizes and nutritional information are only an estimate and may vary from your results.
This recipe was originally published on January 5, 2018 and was updated on January 11, 2019.
Beth
Roasted onions are so yummy! I like the seasonings and how juicy it is. This is such a delightful treat.
Emma
Thank you, Beth! These roasted onions really are nice.