French Onion Soup-Strata

Let's Cook

1. Step 1.

   Preheat the oven to 350°F.

2. Step 2.

   In a large bowl, whisk together 6 large eggs, 1½ cups whole milk, 2 tablespoons Dijon mustard, and 1 tablespoon Worcestershire sauce. Season with salt and pepper to taste. Fold in the sourdough bread cubes (about 1 pound, cut into 1-inch cubes) and let them soak, gently stirring occasionally, while you prepare the onions.

3. Step 3.

   Melt 3 tablespoons unsalted butter in a 10-inch oven-safe skillet over medium-low heat. Add 2 thinly sliced large sweet onions and cook, stirring often, until deep golden brown, about 25 minutes. Stir in 4 minced medium cloves garlic and 1 teaspoon chopped fresh thyme (or ¼ teaspoon dried) and cook until fragrant, about 1 minute. Season with salt and pepper. Increase heat to medium, add ¼ cup dry sherry and ½ cup dry white wine, and cook until the liquid has almost evaporated, about 4 minutes.

4. Step 4.

   Transfer the onion mixture from the skillet to a large plate or bowl. Rub the skillet with additional butter.

5. Step 5.

   Add half of the soaked bread to the skillet and top with half of the onions and half of the shredded Gruyère cheese (about 3 ounces). Layer the remaining bread on top and drizzle with any remaining egg mixture. Scatter with the remaining onions and cheese.

6. Step 6.

   Transfer the skillet to the oven and bake until the bread is crisp and the custard is just set, 40 to 50 minutes. Let cool for 10 minutes before serving.