Grease an 8-inch square baking dish. Cut each half of the English muffins into 6 pieces. Add half of the cubed English muffins in a single layer. Top with half of the sausage and ½ cup of the cheese. Layer the remaining English muffins and sausage and ½ cup more cheese.
Whisk together the eggs, milk, salt, and pepper in a medium bowl until combined. Pour the egg mixture evenly over the casserole. Wrap the baking dish with plastic wrap and place refrigerate for at least 1 hour, or up to 1 day.
Bake at 325 degrees 45 to 50 minutes.
