In a large mixing bowl, whisk together 8 large eggs, 2 cups of milk, 1 teaspoon of salt, 1/2 teaspoon of black pepper, and 1 tablespoon of dry mustard until well combined.

In a skillet over medium heat, cook 1 pound of breakfast sausage until well-browned and crumbly, about 7-10 minutes. Drain excess grease and set aside to cool.

Grease a 9x13-inch baking dish. Layer 6 slices of cubed bread across the bottom, then sprinkle the cooked sausage evenly.

Pour the prepared egg mixture evenly over the bread and sausage, making sure the bread is fully saturated.

Sprinkle 2 cups of shredded cheddar cheese over the top.

Cover the baking dish with plastic wrap and refrigerate for at least 8 hours or overnight.

Preheat your oven to 350°F (175°C). Remove the plastic wrap and bake uncovered for about 45 minutes, until the top is golden brown.

Let the casserole cool for 5-10 minutes before slicing and serving.