Preheat oven to 400F and move the rack to the middle position. Season pork chops generously with salt and pepper.
Add the olive oil to a large, oven-proof skillet on medium-high heat. Once the oil is hot, sear the pork chops for 4-5 minutes on each side (don't move them around until it's time to flip them) until they're nicely golden/browned. Turn the heat down if they start to splatter a lot. Remove chops from the pan and set aside.
Add the butter and onions to the pan and cook for 2 minutes.
Add the mushrooms and cook for 5 minutes, stirring occasionally.
Add the whiskey and garlic, and cook for 3 minutes.
Add the cream, nutmeg, Worcestershire sauce, and peppercorns (if using). Put the pork chops back in the pan.
Place the skillet in the oven until the pork chops are cooked through and reach an internal temperature of 145F in the thickest part. The timing will really depend on how thick your pork chops are and how cool they were when you added them back into the pan (10-15 minutes is a good starting point for 1" thick chops. If you find they're still not done, continue cooking and check every few minutes.). If your pork chops are thinner than 3/4 inch, I would suggest checking them before 10 minutes so you don't overcook them.
Season with extra salt & pepper if needed. Serve immediately. These are delicious with mashed potatoes (try colcannon for an Irish twist).