Cook the sausage in a skillet over medium heat, breaking it into small crumbles, until browned and cooked through. Drain it well and cool for 10 minutes.
Butter a 9-by-13-inch baking dish. Spread in half the bread, sausage and cheddar, then repeat the layers.
Whisk the eggs, milk, salt, dry mustard, pepper and garlic powder until completely blended. Pour slowly over the bread and press the cubes down once.
Cover and refrigerate for at least 8 hours and up to 16 hours. Set the dish at room temperature for 30 minutes while the oven heats to 350°F.
Bake uncovered for 50 to 55 minutes, until puffed, golden and 160°F in the center. Rest for 10 minutes before cutting into 10 squares.