Here's an easy do-ahead breakfast or brunch dish that's great for a large gathering. Dozens of variations are possible: substitute cubes of ham for the sausage, add a layer of sautéed vegetables such as peppers or asparagus, or make a vegetarian version by eliminating the meat.
The night before serving, butter a 9x13-inch baking pan or a 2-quart oven-proof casserole dish. Arrange the cubed bread on the bottom of the buttered pan.
In a large bowl, mix 1 cup of the cheese with the mustard, paprika, and sour cream. Add the sausage and spread the mixture over the bread.
In another bowl, whisk the eggs with the milk, salt, and pepper. Pour the custard into the pan and sprinkle evenly with the remaining cheese. Cover the pan with plastic wrap and refrigerate overnight.
Before baking, position a rack in the middle of the oven and preheat to 350 degrees F. Remove the plastic wrap and transfer the casserole to the oven. Bake until the casserole is puffed, set, and golden, 40 to 50 minutes.
Remove from the oven and let sit at room temperature for 15 minutes before cutting and serving.