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holding one of the marinated red onions on a spoon

Make Ahead Marinated Red Onions

  • Author: Brooke
  • Prep Time: 10 minutes
  • Cook Time: 1 hour 15 minutes
  • Total Time: 1 hour 25 minutes
  • Yield: 8 servings 1x


Make ahead marinated red onions is a healthy recipe that's also super easy.  The red onions are marinated in balsamic vinegar, brown sugar, and other seasonings, then roasted in the oven.  This popular dish is low carb, gluten free, and has many health benefits.  Just start this simple side dish the night before your next potluck, family gathering, or holiday meal.



For the Marinade

  • 1 cup water (236 ml)
  • 1/2 cup sherry vinegar (118 ml)
  • 1/2 cup white balsamic vinegar (118 ml)
  • 2 tablespoons light brown sugar, packed
  • 1 heaping teaspoon fresh rosemary, chopped
  • 1/2 teaspoon salt
  • 1/8 teaspoon black pepper

For the Roasted Onions

  • 4 large red onions
  • 2 tablespoons salted butter (28g)
  • 1 teaspoon fresh rosemary, chopped
  • a few grinds of black pepper


  1. 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.
  2. 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.
  3. 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.
  4. Cook for 15 minutes more, then take out the pan and baste them with the marinade.  Repeat this step two more times.
  5. 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.


  • 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.
  • Category: Dinner
  • Method: Baked
  • Cuisine: American

Keywords: soak, vinegar



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