01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - Season pork chops on both sides with salt, black pepper, garlic powder, and paprika.
03 - Heat olive oil in a large skillet over medium-high heat. Sear pork chops for 2–3 minutes per side until golden. Transfer to a plate; they will finish cooking in the oven.
04 - In the same skillet, melt butter over medium heat. Add flour and whisk for 1 minute until a smooth roux forms. Gradually whisk in whole milk and heavy cream. Cook, whisking, until slightly thickened, about 3 minutes.
05 - Remove skillet from heat. Stir in shredded cheddar, half the Parmesan, salt, black pepper, and ground nutmeg. Mix until the cheese is melted and sauce is smooth.
06 - Arrange half the sliced potatoes in the prepared baking dish. Top with half the onion. Pour half the cheese sauce over the layer.
07 - Repeat layering with remaining potatoes, onions, and cheese sauce.
08 - Place the seared pork chops evenly over the potatoes. Sprinkle with the remaining Parmesan cheese.
09 - Cover dish tightly with aluminum foil. Bake for 45 minutes. Remove foil and continue baking for 20–30 minutes, until potatoes are tender, sauce is bubbling, and pork reaches an internal temperature of 145°F.
10 - Allow casserole to rest for 10 minutes before serving. Garnish with chopped parsley, if desired.