Place a large skillet over medium-high heat then add the sausage. Cook sausage about 10 minutes, breaking up the meat into pieces with a spoon, until no pink remains.

Add onions and bell pepper and cook an additional 3–4 minutes then add garlic, remove from heat and set aside.

Crack all 12 eggs into a large mixing bowl then beat until uniformly yellow in color. Add milk, salt and pepper then stir to combine. Add the reserved sausage mixture, entire bag of frozen hash browns and 1 cup of shredded cheese. Stir until well combined

Coat a 9" x 13" baking dish with cooking spray then add egg mixture. Spread into an even layer then sprinkle remaining ½ cup of shredded cheese over the top. Cover dish with plastic wrap or aluminum foil and refrigerate overnight.

Preheat oven to 350 degrees, remove casserole from the refrigerator, uncover and allow the casserole to sit at room temperature while oven preheats. Bake 40–50 minutes until center is firm. Remove pan to a wire rack and cool 10 minutes before serving.