Preheat oven to 350°F. Grease a 9 x 13" baking dish and set aside.

Heat heavy large skillet over medium heat. Cook the sausage and onion, stirring often and breaking up the sausage into small pieces. Cook until the sausage is browned throughout. Drain and set aside.

In a very large bowl, combine the potatoes, eggs, cheddar cheese, cottage cheese, Swiss cheese, garlic powder, salt, and pepper.

Add the cooked sausage mixture to the bowl and mix well.

Pour the entire mixture into the prepared baking dish. At this point, you can wrap tightly with plastic wrap and refrigerate overnight, if desired.

Bake in preheated oven for 50-60 minutes or until the eggs are set and the cheese is melted and bubbly. (If the casserole sat in the fridge all night, it may need to bake a bit longer.) Watch and cover with foil if the top starts browning too much in the oven.

Let stand at least 10 minutes before serving.