In a large cast-iron skillet over medium-high heat, cook sausage, breaking it into small crumbles, until browned and cooked through, about 8 minutes.
Sprinkle flour over the cooked sausage and stir to coat, cooking for 2-3 minutes to eliminate the raw flour taste.
Gradually add milk, stirring constantly to prevent lumps, and bring to a simmer.
Add salt, black pepper, and garlic powder, then reduce heat to medium-low and simmer for 5-7 minutes, stirring frequently, until gravy thickens to your desired consistency.
Taste and adjust seasoning as needed, then serve hot over buttermilk biscuits.