Combine 1 cup flour, thyme, onion powder, salt and 1/2 t. pepper in a large plastic zipping bag. Add chicken to bag, one or 2 pieces at a time; shake to coat well. Dip chicken into buttermilk; return to bag and shake to coat.
Heat oil in a large skillet over medium heat. Add chicken and sauté 15 minutes, turning to cook evenly until golden. Reduce heat to medium-low. Cook, uncovered, 35 to 40 more minutes or until chicken is tender and juices run clear when chicken is pierced with a fork.
Remove chicken to paper towels, reserving drippings; cover chicken to keep warm. Stir bouillon, remaining flour and remaining pepper into skillet drippings, scraping up any browned bits. Add milk. Cook and stir over medium heat until thickened and bubbly; cook and stir one more minute. Serve hot gravy over chicken.