Preheat your oven to 350 degrees Fahrenheit. Grease a 9x13-inch baking dish with butter so the casserole does not stick. This simple step also helps create golden edges while baking in the oven.

Place the sausage into a large skillet over medium heat. Break it apart using a wooden spoon while cooking. Continue cooking until the sausage becomes browned and fully cooked with no pink remaining.

Carefully drain extra grease from the cooked sausage using paper towels or a strainer. Let the sausage cool slightly before mixing it into the casserole. This keeps the eggs from cooking too early.

In a large mixing bowl, whisk together the eggs, whole milk, salt, black pepper, and garlic powder. Keep whisking until everything looks smooth and fully combined for an even casserole texture.

Place the cubed bread into the greased baking dish. Sprinkle the cooked sausage evenly across the bread pieces. Add shredded cheddar cheese and chopped green onions to create layers of flavor.

Slowly pour the egg mixture over the bread, sausage, and cheese. Press the bread down gently using a spoon so it absorbs the liquid evenly. This helps create a soft and fluffy casserole.

Allow the casserole to sit for about 10 minutes before baking. This resting time helps the bread soak up the egg mixture properly, giving the casserole a rich and creamy texture after baking.

Place the baking dish into the preheated oven and bake for about 45 minutes. The casserole should look golden brown on top, and the center should feel firm when lightly touched.

Remove the casserole carefully from the oven and let it cool for several minutes. Slice into squares and serve warm. The melted cheese and savory sausage make every bite comforting and delicious.