Heat a large cast-iron skillet over medium-high heat. Add the sausage and cook until browned, crumbly, and no longer pink. Remove the sausage from the skillet with a slotted spoon, reserving the drippings in the skillet.
Sprinkle the flour into the pan drippings and whisk until combined. Cook for 2 minutes or until the mixture is bubbly and begins to smell nutty.
Gradually whisk in the milk, cooking until the mixture is bubbly and thickened, about 5 minutes.
Return the sausage to the skillet, stirring until warmed through. Add the garlic powder and season with salt and pepper to taste.
Spoon the gravy over biscuits or onto servings of grits. Sprinkle with parsley before serving, if desired.