Sausage and Potato Breakfast Casserole

From Epicurious

1 lb bulk breakfast sausage
2 Tbsp all purpose flour
1 1/2 C milk (do not use low fat or nonfat)
1 1lb package frozen shredded hashbrown potatoes
4 green onions, finely chopped
1 1/4 C grated sharp cheddar cheese

Preheat oven to 350°F. Butter 8x8x2-inch glass baking dish. Cook sausage in heavy large skillet over medium-high heat until brown, breaking into small pieces with back of spoon, about 5 minutes. Mix in flour, then milk. Cook until mixture thickens and comes to boil, stirring occasionally, about 5 minutes.
Arrange potatoes in prepared dish. Top with 1/3 of green onions, 1 cup cheese, 1/3 of green onions, sausage mixture and remaining 1/4 cup cheese.
Bake casserole until potatoes are tender, about 45 minutes. Sprinkle with remaining green onions and serve.