In a large skillet, heat a drizzle of oil over medium heat. Add the breakfast sausage, breaking it into small pieces, and cook for about 8-10 minutes until browned and cooked through. Once done, transfer the sausage to a plate to cool.

In a spacious mixing bowl, crack in the eggs and pour in the milk and sour cream. Whisk together until the mixture is smooth and slightly frothy—this takes about 2-3 minutes. Add salt and black pepper to taste.

Grease a 9x13-inch baking dish generously with cooking spray or butter. Start by spreading half of the hash browns evenly across the base of the dish. Then, add half of the cooked sausage, followed by a sprinkle of cheddar cheese.

Next, repeat the layering process by placing the remaining hash browns over the first layer uniformly. Follow this with the rest of the sausage and top it off with the remaining cheddar cheese.

Carefully pour the whisked egg mixture over the layered ingredients, ensuring it seeps evenly throughout the layers. Allow the mixture to soak into the layers for a few minutes.

Cover the dish tightly with aluminum foil or plastic wrap and refrigerate overnight.

The next morning, preheat your oven to 350°F (175°C).

Once preheated, remove the cover from your dish and place it in the oven. Bake for 45 minutes covered, then uncover it and bake for an additional 20-25 minutes until golden brown and the center is set.

After baking, let the casserole cool for a few moments before serving. Sprinkle chopped green onions over the top.