Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish with butter.
In a large skillet, cook the sausage over medium heat until browned and cooked through. Do not drain.
Sprinkle flour over the sausage, stirring for 1–2 minutes to coat. Gradually whisk in the milk until smooth.
Simmer until thickened into gravy, about 5 minutes. Season with garlic powder, onion powder, salt, and pepper. Set aside.
Spread the thawed hashbrowns evenly into the bottom of the prepared dish. Layer the quartered biscuits on top of the hashbrowns.
In a separate bowl, whisk the eggs with a pinch of salt and pepper. Pour evenly over the biscuits and hashbrowns.
Sprinkle shredded cheddar cheese over the top. Pour the sausage gravy evenly over the entire casserole.
Bake uncovered for 40–45 minutes, or until the eggs are set and the top is golden and bubbly.
Let cool for 5 minutes before slicing. Garnish with fresh parsley and serve warm.
