Preheat your oven to 350°F (175°C) and lightly grease a 9x13 inch baking dish.

In a large skillet over medium heat, cook the breakfast sausage until browned and fully cooked (about 5-7 minutes). Drain any excess fat.

Reduce heat to low, add cream cheese to the hot sausage, and stir until melted and combined (2-3 minutes).

In a separate bowl, whisk together eggs, milk, garlic powder, onion powder, salt, and pepper until well blended (about 2 minutes).

Spread thawed hashbrowns evenly in the bottom of the baking dish and press down gently (about 3 minutes).

Spoon the sausage and cream cheese mixture evenly over the hashbrowns.

Pour the whisked egg mixture over the casserole to cover all corners.

Sprinkle the sharp cheddar and mozzarella cheeses generously on top.

Bake uncovered for 40-45 minutes until the eggs are set and the top is golden brown.

Let the casserole rest for 5-10 minutes before garnishing with chopped chives or green onions.