Caramelize the Onions. Start by caramelizing the onions. In a large skillet, melt butter over medium heat. Add the sliced onions and cook, stirring occasionally, for about 25-30 minutes until the onions are soft, golden, and caramelized. Add the garlic and thyme during the last 5 minutes for extra flavor.
Sear the Pork Chops. While the onions are caramelizing, season the pork chops generously with salt and pepper. Heat olive oil in another large skillet over medium-high heat. Sear the pork chops for about 3-4 minutes on each side until they’re nicely browned. Remove from the skillet and set aside.
Make the Sauce. After the pork chops are seared, add a little more butter to the skillet. Stir in flour and cook for 1 minute. Slowly add the beef broth, whisking to avoid lumps, and let the sauce simmer until it thickens slightly.
Assemble the Dish. Return the caramelized onions to the skillet with the sauce and stir to combine. Place the seared pork chops on top of the onions. Sprinkle the mozzarella and Gruyère cheese over the pork chops.
Bake to Perfection. Preheat your oven to 375°F. Transfer the skillet to the oven and bake for about 15-20 minutes, or until the pork chops are fully cooked and the cheese is bubbly and golden.
Garnish and Serve. Remove the skillet from the oven and garnish with a sprinkle of fresh thyme. Serve the French Onion Pork Chops hot, with the delicious caramelized onions and sauce spooned over the top.