Preheat and prepare baking dish: Preheat your oven to 375°F (190°C). Grease a 9x13-inch ceramic or glass baking dish generously with nonstick cooking spray or butter.

Brown the breakfast sausage: In a large skillet over medium-high heat, cook the ground breakfast sausage, breaking it into bite-sized crumbles with a wooden spoon for 5 to 6 minutes until browned and cooked through. Add the diced onion and red bell pepper during the last 2 minutes of cooking. Stir in minced garlic for 30 seconds. Remove from heat and drain excess grease.

Layer the hashbrowns: In a large bowl, toss the thawed shredded hashbrowns with 1/4 cup of melted butter, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Press the hashbrown mixture evenly into the bottom of the prepared 9x13 baking dish.

Add sausage and cheeses: Scatter the browned sausage and pepper mixture evenly over the hashbrown layer. Top with 1.5 cups of the shredded sharp cheddar cheese and 1 cup of Monterey Jack cheese.

Whisk the egg custard: In a large glass batter bowl, whisk together the eggs, whole milk, heavy cream, garlic powder, onion powder, smoked paprika, remaining 1/2 teaspoon salt, and 1/4 teaspoon black pepper until completely smooth and frothy.

Pour and bake: Pour the egg mixture slowly and evenly over the layered casserole, ensuring it seeps through into the hashbrowns. Sprinkle the remaining 1/2 cup of sharp cheddar cheese on top. Bake uncovered for 40 to 45 minutes until the center is set (a knife inserted into the center comes out clean) and the top is golden-brown and bubbling.

Rest, slice and serve: Remove from the oven and let rest for 10 minutes so the layers settle and slice cleanly into gorgeous squares. Garnish with fresh chives and sliced green onions. Serve warm with coffee, fresh fruit, or hot sauce!