Preheat oven to 350°F. Pat chicken pieces dry with paper towels.
In a shallow dish, combine flour, salt, pepper, garlic powder, and thyme. Dredge each chicken piece in the seasoned flour mixture.
Heat vegetable oil in a large oven-safe skillet or Dutch oven over medium-high heat. Sear chicken pieces skin-side down for 4-5 minutes until golden brown, then flip and sear another 3-4 minutes. Remove chicken and set aside.
Add sliced onions to the same skillet and cook for 5 minutes until softened. Add chicken broth and butter, scraping up any browned bits from the bottom of the pan.
Return chicken to the skillet, cover, and transfer to the oven. Bake for 75-90 minutes until chicken is tender and cooked through.
Remove chicken to a serving platter. Place skillet on stovetop over medium heat, stir in heavy cream, and simmer gravy for 3-4 minutes until slightly thickened.
Pour gravy over chicken, garnish with fresh parsley, and serve with mashed potatoes or biscuits.