Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish with butter or non-stick spray.

In a large skillet, cook the breakfast sausage over medium heat until browned and cooked through, breaking it into crumbles. Drain excess fat and set sausage aside, reserving drippings for gravy.

In a large bowl, whisk together eggs, milk, salt, and pepper until fully combined.

Spread the thawed hash browns evenly in the prepared baking dish. Sprinkle cooked sausage over the hash browns, then pour the egg mixture evenly on top.

Sprinkle shredded cheddar cheese over the casserole. Bake uncovered for 35-40 minutes or until eggs are set and the top is golden.

While the casserole bakes, prepare the biscuits. In a medium bowl, combine flour, baking powder, sugar, and salt. Cut in cold butter with a pastry blender or fork until mixture resembles coarse crumbs.

Stir in milk just until dough forms. Turn dough onto a floured surface, knead gently 3-4 times, and pat into a 1-inch thick round. Cut biscuits with a round cutter and place on a baking sheet.

Bake biscuits in the oven alongside the casserole for 12-15 minutes or until golden brown.

To make the gravy, heat reserved sausage drippings in a skillet over medium heat. Whisk in flour and cook for 1-2 minutes until lightly browned.

Gradually whisk in milk and cook, stirring constantly, until gravy thickens. Season with salt and pepper to taste.

Serve the breakfast casserole warm with freshly baked biscuits topped with sausage gravy.