In a large skillet, heat the pan over medium heat and cook the breakfast sausage, breaking it into crumbles until it turns golden brown, about 8-10 minutes.

In a spacious mixing bowl, whisk together 8 large eggs, 2 cups of milk, 1 cup of sour cream, salt, and pepper until well combined and smooth.

Grease a 9x13-inch baking dish with cooking spray or butter. Spread half of the hash browns evenly across the bottom of the dish to create a base layer.

Sprinkle half of the cooked sausage over the hash brown layer, followed by a generous handful of shredded cheddar cheese.

Add the remaining hash browns as a second layer, distributing them evenly. Top with the rest of the sausage and another sprinkle of cheddar cheese.

Carefully pour the egg mixture over the layered ingredients in the baking dish.

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

Preheat your oven to 350°F (175°C). Remove the cover and bake the casserole for 45 minutes. Uncover and bake for an additional 20-25 minutes until the top is golden brown and the center is set.

Once baked, remove the dish from the oven and let it cool slightly. Sprinkle chopped green onions on top before serving.