Prepare the chicken: Trim excess fat. For even marination, butterfly thick breasts or use a meat mallet to create uniform thickness (approximately ¾-inch).
Create the marinade base: In a large bowl, whisk the buttermilk and salt until the salt begins to dissolve.
Add dry components: Whisk in garlic powder, onion powder, paprika, black pepper, thyme, and cayenne (if using). Ensure even distribution with no clumping.
Incorporate oil: Slowly drizzle in oil while whisking continuously to create a light emulsion.
Combine chicken and marinade: Place chicken pieces in a container or zip-top bag. Pour marinade over chicken, ensuring all surfaces make contact with the liquid. Massage gently to distribute marinade.
Refrigerate: Seal container and refrigerate. For whole chicken breasts, marinate 4-24 hours (8 hours optimal). Turn chicken halfway through if not fully submerged.
Remove and prepare for cooking: Remove chicken from marinade, allowing excess to drip off. Do not rinse. Pat very gently with paper towels to remove excess surface moisture for better browning.