Preheat oven to 400 F degrees. Melt butter and olive oil in a large cast iron or other oven safe skillet, over MED-HIGH heat. Add sliced onions and saute 3-5 minutes, until soft. Add 4 Tbsp beef stock and continue to cook, stirring occasionally, for 12-15 minutes, until onions are extremely tender and golden brown.
As onions are sautéing, season both sides of pork chops with salt, black pepper, thyme and garlic powder. Transfer onions to a plate, do not wipe out skillet.
Reduce heat to MED, add a drizzle of olive oil to the skillet if needed, and cook pork chops, about 3-4 minutes per side, until golden brown.Transfer pork chops to plate.
Return cooked onions to pan and sprinkle with flour. Stir to coat and cook about a minute. Add remaining 1 cup beef stock and stir often until mixture comes to a boil. Season with a pinch of salt and pepper.
Nestle pork chops back into the pan, spooning some of the beef stock over the tops of the chops. Top with a slices of provolone cheese, and a mound of the shredded gruyere (about a ¼ cup on each chop).
Add a few sprigs of fresh thyme and add skillet to oven and bake 8-10 minutes, until cheese is melted and gooey. Before serving, spoon some of the beef stock/onion mixture over the top of the cheese, and garnish with some additional black pepper if desired.