Use up any leftover baked ham in this easy breakfast casserole. The night before you want to serve the strata, cook the mushrooms with onions and thyme and stir them into a mixture of eggs, milk, and Dijon mustard. Add bread cubes, Gruyère cheese, and ham, dump the whole thing into a baking dish, and let it soak overnight. In the morning, bake for about an hour and you’ll have a hearty brunch dish to serve with a colorful fruit salad and mimosas.
3 tablespoons unsalted butter
1 cup medium-dice yellow onion
1 pound medium cremini mushrooms, stems trimmed and quartered
1 teaspoon dried thyme
12 large eggs
2 1/2 cups whole milk
1/3 cup Dijon mustard
3/4 teaspoon kosher salt, plus more as needed
1/2 teaspoon freshly ground black pepper, plus more as needed
12 ounces cooked ham, casing trimmed and cut into 1/2-inch dice
8 ounces French or Italian bread, cut into 3/4-inch cubes (about 6 cups)
1 1/2 cups shredded Gruyère cheese (about 3 1/2 ounces)
Melt the butter in a large frying pan over medium heat, add the onion, season with salt and pepper, and cook until softened, about 6 minutes. Add the mushrooms and thyme and cook, stirring rarely, until the mushrooms are lightly browned in spots and all of the moisture has evaporated, about 10 minutes. Remove the pan from the heat.
Place the eggs in a large bowl and whisk until they’re broken up. Add the milk, mustard, and measured salt and pepper and whisk to combine. Add the ham, bread, cheese, and sautéed mushroom mixture and stir to combine. Pour into a 13-by-9-inch baking dish and arrange into an even layer. Cover the dish with plastic wrap or aluminum foil and refrigerate overnight.
Heat the oven to 350°F and arrange a rack in the middle. Meanwhile, remove the strata from the refrigerator and let it sit at room temperature.
Remove the plastic wrap or aluminum foil from the strata and bake until a toothpick inserted into the center comes out clean, about 1 hour. Remove the dish to a wire rack and let it cool for 10 minutes before serving.