Delicious and Easy Red Onion Gratin

Red Onion Gratin ~ this unusual gratin is perfect for any fall or holiday meal, the red onion bakes up soft and sweet in a cheesy sauce finished off with a crunchy herb crumb topping.

Red Onion Gratin 3

I love all members of the onion family, from shallots and green onions, to leeks, Vidalias, Maui, and just plain old reds. I’m always looking for ways to cast them in the leading role, rather than burying them in the first few steps of a recipe. Onions are cheap and healthy, and so good tasting, they deserve better. Red Onion Gratin is a simple side dish that’s fancy enough for company, and goes with just about any meat, chicken or fish. I’d say it’s absolutely made to have with a good steak.

Red Onion Gratin 1

This gratin looks nice and rustic in a skillet, but you can use any gratin or baking dish you have. Allow two or three  slices of onion per person. I used all red onions, but you can easily use white, or a mix. Sweet onions like Vidalia or Maui would be great, too.

Grilled Red Onions

Giving the onions a quick grilling not only gives them extra smokey flavor, but it softens them a little so they don’t need too much time in the oven. The beautiful grilled slices get laid out over a basic sherry laced bechamel cream sauce, and then covered with Gruyere and fresh breadcrumbs.

Red Onions in Bechamel Sauce

The result is pure heaven!

Red Onion Gratin in skillet

red onion gratin in a cast iron skillet
3.25 from 4 votes

Red Onion Gratin

Course Side Dish
Cuisine American, French
Author Sue Moran


  • 2 red onions
  • olive oil for brushing
  • 2 Tbsp unsalted butter divided
  • 1 Tbsp all purpose flour
  • 2/3 cups heavy cream
  • 3 Tbsp dry sherry
  • salt and fresh cracked black pepper
  • dash of nutmeg I grate mine fresh
  • handful of fresh thyme
  • 1 cup shredded Gruyere cheese
  • 1/2 cup fresh breadcrumbs


  • Set oven to 400F
  • Peel and thickly slice the onions.
  • Heat a grill pan until quite hot, and brush the onion slices lightly with olive oil. Grill the slices for a minute or two on each side so that they get slightly softened and have nice grill marks. Set them aside.
  • In a saucepan, heat 1 Tbsp of the butter over medium heat, and stir in the flour. Cook for a minute, stirring constantly. Pour in the cream and sherry and whisk until smooth. Stir constantly while the mixture comes up to a simmer and is thickened. Add salt and pepper to taste and the dash of nutmeg.
  • Pour the sauce into a cast iron skillet or gratin dish. Arrange the onion slices over the sauce.
  • Sprinkle the cheese evenly over all.
  • Stir the breadcrumbs together with the last tablespoon of melted butter, and a little salt, pepper, and a few thyme leaves. Sprinkle the breadcrumbs over the cheese,
  • Bake for about 20 minutes until browned and bubbling. You can run the gratin under the broiler at the last minute if you want extra browning,

Cook's notes

This recipe was inspired by The Proud Italian Cook
The nutritional information for recipes on this site is provided as a courtesy and although tries to provide accurate nutritional information, these figures are only estimates.


Don’t forget to pin this versatile Red Onion Gratin!

Red Onion Gratin ~ the onion bakes up soft and sweet in a cheesy sauce finished off with a crunchy herb crumb topping in this unusual gratin! #sidedish #redonions #gratin #casserole #onioncasserole #bakedonions #vegetarian #holidaysidedish #easysidedish #vegetable #onions #oniongratin

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    Leave a Reply

    Please rate this recipe!

  • Reply
    Laura (Tutti Dolci)
    December 13, 2013 at 9:48 pm

    I’ve tried various gratins but never one with onions – love!

  • Reply
    December 13, 2013 at 2:40 am

    love this idea… such a novel way to prep onions… very pretty x

  • Reply
    Maria | Pink Patisserie
    December 12, 2013 at 5:05 pm

    I could stick my whole face in that! Looks scrumptious!!

  • Reply
    December 12, 2013 at 9:22 am

    Of course, why not? An onion gratin! So perfect!

  • Reply
    December 12, 2013 at 9:16 am

    I love the idea of elevating the humble onion to a much over-looked, but well deserved, side dish status.
    Yum for dinner in my book with anything… even a toasted slice of hearty bread.
    Great photos.

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