PreheatSet your oven to 350°F (175°C). If you’ve ever tried baking a casserole in a cold oven… yeah, it never ends well.
Cook the SausageBrown the breakfast sausage in a skillet over medium heat until fully cooked. Drain the grease and set aside.(If it smells so good you’re tempted to eat a spoonful—don’t worry, we’ve all been there.)
Build the BaseGrease a 9×13 inch baking dish. Scatter the frozen hash browns evenly across the bottom.
Layer the FlavorAdd the cooked sausage, followed by cheddar, mozzarella, bacon, and scallions. You’re basically constructing a flavor lasagna here.
Make the Egg MixtureIn a large bowl, whisk the eggs, milk, garlic powder, onion powder, salt, and pepper. It should look slightly frothy—kind of like you’re making a latte for someone you love.
Pour It InPour the egg mixture slowly and evenly across the casserole.Press down gently with a spatula so everything settles into the custard.
BakeCover the dish tightly with foil and bake for 35–40 minutes, or until the center looks set and no longer jiggles aggressively when you tap the side.
RestRemove from the oven, uncover, and rest for 5 minutes. This helps it slice cleanly instead of collapsing into delicious breakfast rubble.
ServeCut into squares and serve while warm. Coffee or OJ on the side highly recommended.