Get campfire rolling. Add sausage into cast iron and with a wooden spatula break up sausage into smaller pieces. Cook until brown and fully done (about 8 minutes). Place butter in skillet and stir until melted. Sprinkle flour, cornstarch, garlic, and pepper on top of the sausage and slowly stir until well coated and grease is full absorbed. Continue stirring and let the flour cook fully for about 2 minutes. While stirring, slowly pour in the milk. Continue to stir and simmer until gravy thickens (3 to 5 minutes). Serve over warm fresh biscuits.