Pat the pork chops dry with a paper towel to remove excess moisture. Season both sides of the pork chops evenly with ½ teaspoon salt and ½ teaspoon black pepper, or more to taste.
Heat 1 tablespoon olive oil in a large heavy-bottomed skillet (such as cast iron) over medium-high heat. Once the oil is shimmering but not smoking, carefully add the pork chops to the pan.
Sear for 4-5 minutes per side, undisturbed, until a deep golden-brown crust forms. Then, transfer the seared pork chops to a plate and loosely tent with foil to keep warm
Reduce the heat to medium, then add 1 tablespoon of salted butter to the same skillet. Once melted, add the thinly sliced onion and cook, stirring occasionally, for 5-6 minutes, until softened and lightly caramelized.
Stir in the sliced apples and minced garlic, and cook for 2-3 minutes until the apples are slightly softened but still hold their shape.
Pour in ½ cup low-sodium chicken broth and ¼ cup apple cider (or apple juice), stirring to deglaze the pan and scrape up any browned bits from the bottom. Then, stir in 1 tablespoon of Dijon mustard, 1 tablespoon of brown sugar, and 1 tablespoon of freshly minced thyme (or 1 teaspoon of dried thyme).
Bring the sauce to a gentle simmer and let it cook for 2 minutes to meld the flavors.
Return the seared pork chops to the skillet, nestling them into the sauce and apples. Spoon a little sauce over the chops, cover the pan, and let them cook for 8-12 minutes, or until they reach an internal temperature of 140°F (63°C) when measured with a meat thermometer.
Once cooked, remove the pan from heat and let the pork chops rest for 5 minutes to retain their juices. Garnish with fresh thyme sprigs, if desired.