In a large skillet set over medium heat, cook the sausage, using a wooden spoon to break up the meat, for 8-10 minutes, until cooked trough.
Add the sage, thyme, and garlic powder and cook for 1 minute more.
Sprinkle the flour over the sausage and stir until the flour is absorbed, about 2 minutes.
Reduce the heat to low and, while whisking constantly, until thick, about 4 minutes. Cook it longer if you like thick gravy, or add the remaining 1/2 cup of milk, if needed, to thin it out.
Remove the pan from heat. Season with salt and pepper. Serve warm.