Preheat a skillet over medium heat. Add the breakfast sausage and cook, breaking it up with a spoon, until browned and fully cooked, about 7-8 minutes. Drain excess grease and set aside.
In a large mixing bowl, whisk together the eggs, whole milk, salt, black pepper, and garlic powder until well combined.
Grease a 9×13 inch baking dish. Spread half of the cubed bread evenly in the dish.
Sprinkle half of the cooked sausage over the bread layer.
Sprinkle half of the shredded cheddar cheese over the sausage.
Repeat layering with the remaining bread cubes, sausage, and cheese.
Pour the egg mixture evenly over the layered ingredients, pressing down gently to ensure the bread absorbs the liquid.
Cover the baking dish tightly with aluminum foil.
To freeze: Place the covered casserole in the freezer for up to 3 months.
To bake from frozen: Preheat the oven to 350°F (175°C). Remove the foil and bake uncovered for 60 minutes or until the casserole is set and the top is golden brown.
Let the casserole cool for 5 minutes before serving.