Pat the pork chops dry then season them with sea salt, freshly cracked pepper, garlic powder, and fresh thyme, to taste, on both sides; set aside.
Heat the butter in a large oven-proof cast iron skillet over medium heat. Add the onions and cook, stirring often, for 20 minutes, until softened and golden brown, and caramelized. Side Note: If the skillet gets dry while cooking and the onions are getting burned add a bit of water, you want them to cook slowly, not get charred.
Remove the caramelized onions from the skillet and set them aside.
Drizzle the olive oil in the skillet and heat over high heat. Add the seasoned pork chops and cook for about 2-3 minutes, or until golden brown then flip them over and cook for another 2-3 minutes, or until golden brown; remove from the skillet and set on a plate. At this point, the pork is not cooked through.
Turn the heat to medium and return the onions to the skillet along with the minced garlic and fresh thyme leaves. Cook, stirring constantly, for 1 minute.
Add the flour and cook, stirring constantly, for 2 minutes.
Stir in the wine and mix well.
Stir in the broth, Worcestershire sauce, and Dijon mustard. Mix until well combined. Season with sea salt and freshly cracked pepper, to taste.
When the sauce comes to a simmer, nestle the pork chops in the sauce. Cover the skillet with a lid and cook for about 5-7 minutes, or until the pork reaches a temperature of 145-150, for medium-rare.
Top the chops with Gruyere then place in the oven under the broiler until the cheese is melted, gooey, and a bit golden.
Remove from the oven then add fresh thyme sprigs and some fresh parsley to the top. Serve immediately.