Preheat the oven to 350. Spray a 9x13-inch glass baking dish with non-stick cooking spray.
Brown and drain the ground sausage.
To the prepared baking dish, add the torn English muffins and browned sausage.
In a large mixing bowl, whisk the eggs, milk, spicy mustard and salt and pepper. Pour the egg mixture over the bread and sausage. Top with shredded cheese. (Option: cover with plastic wrap and let sit in the fridge overnight.)
Bake in the preheated oven for 45 to 50 minutes, or until eggs are set and cooked through in the middle. I sometimes cover mine with foil the last 15 minutes of baking, to keep it from getting overly brown on top.
Serve Egg McMuffin Casserole with side of fresh fruit.