Gather all the ingredients: 1 pound bulk pork sausage, 8 large eggs, 2 ½ cups milk, 1 teaspoon salt, 1 teaspoon ground mustard, 6 slices white bread (cut into ½-inch cubes), 1 cup shredded Cheddar cheese, and cooking spray.

Heat a large skillet over medium-high heat, add the sausage, and cook for about 10 minutes until it is crumbly, evenly browned, and no longer pink. Drain and discard any excess grease.

In a large bowl, beat the 8 large eggs. Stir in 2 ½ cups of milk, 1 teaspoon of salt, and 1 teaspoon of ground mustard until well combined.

Fold the 6 slices of bread cubes, 1 cup of shredded Cheddar cheese, and the cooked sausage into the egg and milk mixture. Ensure all ingredients are evenly incorporated.

Lightly grease a 7×11-inch baking dish with cooking spray. Pour the egg mixture into the prepared dish, spreading it out evenly. Cover the dish and refrigerate for 8 hours or overnight to allow the flavors to meld and the bread to absorb the liquid.

Preheat the oven to 350°F (175°C). Remove the casserole from the refrigerator 30 minutes before you plan to bake it to let it come to room temperature.

Bake the casserole in the preheated oven for about 40 minutes, or until a knife inserted near the center comes out clean. Once done, remove from the oven, let it cool for a few minutes, and then serve your delicious sausage and egg breakfast casserole hot.