A breakfast casserole can be as simple or deluxe as you like, but the template stays more or less the same. A basic ratio is one egg to a half-cup of liquid dairy (milk, cream or a combination) to a cup of cubed bread. Substituting yolks for some of the whole eggs will give you a richer custard. Using fewer eggs gives you a firmer casserole that’s easier to slice for serving. And mixing in plenty of grated cheese (about a half-cup per cup of dairy) adds flavor, luscious gooeyness and a scattering of browned bits on the top.
As for the bread, the lighter the loaf, the more ethereal the casserole. Think brioche, challah, good white bread or children-friendly soft whole-wheat (nothing too hearty, seedy or grainy). The more stale and dried out it is, the more custard it can absorb. Many recipes call for drying out fresh bread in a low oven. But if you toast the bread in a very hot oven instead, you’ll both dry it out and give it a deep caramelized flavor.
In this recipe, I use toasted croissants, which makes the casserole particularly buttery and rich. Other than that, I stick close to the classic combination of sausage and Gruyère. But feel free to play around and substitute cooked bacon or cubed ham for the sausage, and another kind of cheese for the Gruyère. You can add sautéed or roasted vegetables if you like (spinach, mushrooms, cherry tomatoes), or even small bits of dried fruit that you’ve first simmered in something delectable — figs in port, dried apricots in white wine. It will add a sweet note to contrast with all the savory goodness.
You can even add smoked salmon and cream cheese to a breakfast casserole.
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Buttery Breakfast Casserole
Yield: 8 to 10 servings
1 pound croissants (about 5 to 7), split in half lengthwise
1 tablespoon extra-virgin olive oil, more for baking dish
1 bunch scallions (6 to 7), white and light green parts thinly sliced, greens reserved
3/4 pound sweet Italian sausage, casings removed
2 teaspoons finely chopped fresh sage
8 large eggs
3 cups whole milk
1 cup heavy cream
8 ounces Gruyère, grated (2 cups)
1 1/4 teaspoons kosher salt
1 teaspoon black pepper
Heat oven to 500 degrees. Spread croissants on a large baking sheet and toast, cut side up, until golden brown, 5 to 10 minutes (watch carefully to see that they do not burn). Let cool, then tear into large bite-size pieces.
In a medium skillet over medium-high heat, warm the olive oil. Add sliced scallions and sausage meat; cook, breaking up meat with a fork, until mixture is well browned, about 5 minutes. Stir in sage, and remove from heat.
In a large bowl, toss together croissants and sausage mixture. In a separate bowl, whisk together eggs, milk, cream, 1 1/2 cups cheese, salt and pepper.
Lightly oil a 9- x 13-inch baking dish. Turn croissant mixture into pan, spreading it out evenly over the bottom. Pour custard into pan, pressing croissants down gently to help absorb the liquid. Cover pan with plastic wrap and refrigerate at least 4 hours or overnight.
When you’re ready to bake the casserole, heat oven to 350 degrees. Scatter the remaining grated cheese over the top of the casserole. Transfer to oven and bake until casserole is golden brown and firm to the touch, 45 minutes. Let stand 10 minutes. Garnish with sliced scallion tops before serving.