When you’re ready to make the casserole, preheat your oven to 350°F. Grease a medium baking dish with butter or nonstick spray to prevent sticking and ensure easy serving later.

Lay 6 slices of bread in the bottom of the greased baking dish. This will form the base of your “sandwich” layers. White bread is classic for its soft texture, but you can use any bread you prefer.

Place 1 slice of sharp cheddar cheese on each slice of bread. The cheddar should cover as much of the bread as possible to ensure melty, cheesy goodness in every bite.

Top each cheese-topped bread slice with another slice of bread, creating a total of six sandwiches arranged in the dish.

In a mixing bowl, whisk together the beaten egg yolks or whole eggs with the whole milk, salt, pepper, and dry mustard. The dry mustard adds a subtle tang that enhances the cheddar’s flavor.

Pour the custard mixture evenly over the assembled sandwiches. The bread will gradually soak up the liquid, softening and absorbing the flavors. Cover the dish and chill in the refrigerator until the bread is thoroughly moistened—this step can be as short as 30 minutes or as long as overnight for a richer flavor.

Once the bread is softened, bake the casserole uncovered in the preheated oven for about 1 hour, or until the top is golden brown and the custard is set. You’ll know it’s ready when the top springs back lightly when pressed.

Let the casserole cool slightly before slicing into squares or rectangles. Serve warm with a side salad, tomato soup, or fresh fruit for a complete meal.