Preheat oven to 400°F and grease a 9-inch deep-dish pie plate.

In a large skillet, cook sausage over medium heat until no longer pink. Add garlic and cook 1 minute longer. Drain excess fat.

Stir in 2 cups of shredded cheese and transfer mixture to prepared pie plate.

In a bowl, whisk together milk, eggs, biscuit mix, sage, and pepper until smooth. Pour evenly over sausage mixture.

Bake for 20–25 minutes, or until a knife inserted near the center comes out clean.

Sprinkle remaining cheese on top and bake 1–2 minutes longer until melted. Let stand 10 minutes before slicing.