In a large, lock-top plastic bag, combine the flour, cornstarch, onion powder, garlic powder, 1 teaspoon each salt and black pepper, and cayenne pepper. Seal and shake the bag to mix. Add the pork chops, then seal and shake the bag to coat the chops. In a large frying pan over medium-high heat, melt the butter with the olive oil. Reduce the heat to medium, add the chops (reserving the seasoned flour), and cook, turning once, until browned, about 5 minutes on each side. Transfer to a plate and keep warm.

Add the onions and celery to the frying pan over medium heat and cook for 5-7 minutes. Add ½ cup of the reserved seasoned flour and cook, stirring occasionally, for 3 minutes or until light brown. Raise the heat to medium-high and add the stock. Bring to a boil, stirring constantly and scraping up any browned bits on the pan bottom. Reduce the heat to low, stir in any accumulated juices from the chops, and nestle the meat in the gravy. Cover and simmer over very low heat until the gravy is very thick and the meat is fork-tender, about 1 hour.

Transfer the chops to a warmed platter. Season the gravy with salt and black pepper. Spoon the gravy over the chops and serve.