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French Onion Brioche Strata

This French Onion Brioche Strata is a savory baked dish layered with caramelized onions, toasted brioche, and a rich custard made with eggs, cream, and beef broth. Finished with melted Gruyère and Swiss cheese, it bakes into soft, sliceable loaves with golden edges and a custardy center.
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Prep Time 45 minutes
Cook Time 35 minutes
Total Time 1 hour 20 minutes
Servings: 12 Servings
Course: Breakfast
Ingredients Equipment Method

Ingredients
  

The Onions
  • 5 large yellow onions thinly sliced
  • 4 tbsp unsalted butter
  • 1 tbsp olive oil
  • 1 tsp sugar
  • 2 cloves garlic minced
  • ½ cup dry sherry or white wine
  • 1 tbsp fresh thyme leaves
The Base & Custard
  • 1 large loaf brioche bread cut into 1-inch cubes (about 8-10 cups)
  • 5 large eggs
  • 1½ cups heavy cream
  • 1 cup bone broth
  • 1 tsp dijon mustard
  • 8 oz Gruyère cheese freshly shredded
  • 4 oz swiss or mozzarella shredded
  • salt and cracked pepper

Equipment

  • 3 9x5 loaf pans
  • Large skillet or dutch oven
  • Baking Sheet
  • Large mixing bowl
  • Whisk
  • Measuring cups and spoons
  • Knife & cutting board
  • Aluminum Foil

Method
 

  1. Caramelize your onions in the butter and oil for 30–40 minutes until dark and jammy. Deglaze with the sherry, then add garlic and thyme. Meanwhile, toast your brioche cubes at 350°F for 8–10 minutes until dry and slightly golden.
  2. In a large bowl, whisk the eggs, heavy cream, beef broth, Dijon, salt, and pepper. For accuracy, you can pour this into a large measuring cup, you should have roughly 3 cups of liquid.
  3. Grease three 9x5 inch loaf pans. To keep them even, follow this layering for each pan:
    Bottom Layer: Add about 1.5 cups of toasted brioche, 2 tablespoons of onions, and a handful of cheese.
    Top Layer: Add another 1.5 cups of brioche, 2 tablespoons of onions, and a generous layer of cheese.
    Pour 1 cup of custard slowly over each pan. Press down gently with a spoon to make sure the top cubes are submerged.
  4. Cover the pans with foil and bake at 375°F for 15 minutes. Remove the foil and bake for another 20–25 minutes until the cheese is bubbling and the centers are set.