Step 1

Heat the oven to 375°F and prepare the baking dish. Arrange a rack in the middle of the oven and heat to 375°F. Lightly grease a 9x13-inch baking dish.

Step 2

Whisk the eggs. Place the eggs in a large bowl and whisk until fully beaten.

Step 3

Whisk in the milk, salt, and pepper. Add the milk, salt, and pepper, and whisk until frothy.

Step 4

Add the mix-ins. Stir in any mix-ins such as meat, cheese, vegetables, or herbs. At this point the casserole may be refrigerated overnight, or frozen. (If freezing, thaw overnight before cooking and proceed to bake as directed below.)

Step 5

Bake for 45 minutes. Pour into the prepared baking dish. Bake until puffed around the edges and a tester inserted in the center comes out clean, about 45 minutes.