Grease 13x9" baking dish with cooking spray; set aside until ready to use.
In a large skillet, over medium heat, cook sausage until no longer pink. Drain fat and place in bowl; set aside.
In the same skillet, add hash browns and cook until lightly browned. Place hash browns in bottom of prepared pan. Evenly top with sausage and cheese.
In a large bowl, whisk together eggs, milk, salt, pepper, garlic powder, and onion powder. Pour over hash brown mixture.
At this point, you can bake the casserole at 350ºF for 35 to 45 minutes or cover with plastic wrap and place in the refrigerator overnight.
Notes
Make sure to brown the hash browns correctly! I'm embarrassed to admit this but I had no idea what I was doing and did not brown them right, so my casserole ended up a bit watery. My parents pro tip (yes, I had to ask my parents) was to let one side of the hash browns cook before flipping them over to cook the other side. Do not stir them around! Whoops.