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.

Transfer each piece of chicken from the marinade into the shallow dish one at a time. Make sure the chicken is coated completely.

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).