Brown the sausage in a skillet over medium-high heat, breaking it into crumbles, until cooked through and deeply browned, about 8 minutes. Drain on a paper towel-lined plate.

In a large bowl, whisk the eggs, milk, salt, pepper, garlic powder, and onion powder until smooth. Stir in 1 1/2 cups cheese and all of the sausage.

Grease a 9x13-inch baking dish. Spread the frozen hashbrowns in the dish. Pour the egg mixture on top and press down gently so the liquid soaks into the potatoes. Sprinkle the remaining 1/2 cup cheese over the top. Cover with foil and refrigerate at least 4 hours or overnight.

Preheat oven to 350°F. Uncover and bake 45 to 50 minutes, until the center is set and the top is puffed and golden. Let rest 5 to 10 minutes, then slice and serve.