Heat oven to 350°F; spray a 9x13-inch dish. Cut each biscuit into 6 pieces and arrange in dish.
Cook sausage in a large skillet over medium-high 8-10 minutes until browned and crumbly; retain grease.
Stir in flour to coat; cook 1 minute, stirring constantly.
Gradually stir in 2 cups milk; add salt, 1/2 teaspoon pepper, garlic powder, and optional cayenne. Simmer 3-4 minutes until thickened; remove from heat.
Whisk eggs, remaining 1 cup milk, and remaining 1/2 teaspoon pepper in a large bowl.
Spread gravy over biscuits; add 1 cup cheese, egg mixture, then remaining 1 cup cheese.
Bake 50-55 minutes until eggs fully set and top is golden; cover with foil if browning too quickly.
Cool 10 minutes; garnish with chives. To freeze, cool completely, portion, wrap in plastic and foil, and freeze in a bag up to 2 months. Microwave 3-4 minutes or reheat at 350°F for 25-30 minutes.