Preheat oven to 400ºF. Spray a quarter sheet pan with cooking spray.
Place frozen hash brown patties on the baking sheet and bake for 15 minutes. Remove from the oven.
Reduce oven temperature to 350ºF.
While the potatoes are baking, cook breakfast sausage in a large skillet until no longer pink. Remove from the heat and drain excess grease.
Combine cooked sausage, cream cheese, Rotel diced tomatoes and green chiles in a medium bowl.
Top the partially baked hash brown potatoes with sausage mixture and shredded sharp cheddar cheese.
In a large bowl, whisk together eggs, milk, sour cream, dijon mustard, onion powder, garlic powder, salt and black pepper.
Pour egg mixture over casserole. Cover the dish with aluminum foil.
Bake covered for 20 minutes. Remove foil and bake for an additional 10 to 15 minutes, until the eggs are set.
