Combine the chicken, salt, pepper, garlic, dried mustard, paprika, and sage together in a large bowl. Stir together to coat the chicken evenly. Pour in the buttermilk over the seasoned chicken and stir again until well coated.
Buttermilk fried chicken will keep for 3-5 days in the fridge. It is best reheated in the oven (325 for 10 minutes or until heated through) or the air fryer (325 for about 5 minutes).