Sprinkle pork chops evenly with salt, pepper, and fennel. Let stand at room temperature for 30 minutes.
Heat oil in a 12-inch cast-iron skillet over medium-high. Add pork chops; cook until golden brown, 3 to 5 minutes per side. Transfer to a plate. (Do not wipe skillet clean.)
Add pear slices to skillet, and reduce heat to medium; cook, flipping occasionally, until pear slices are browned and slightly softened, about 6 minutes. Stir in chicken stock, maple syrup, vinegar, mustard, and thyme sprigs. Once simmering, nestle pork chops into skillet, and cook until an instant-read thermometer inserted into thickest portion of meat registers 140°F, 2 to 4 minutes. Transfer pork chops to a plate. Cook sauce until slightly thickened and pear slices are just softened, 2 to 3 minutes; spoon over pork chops. Season with additional salt to taste; garnish with fresh thyme leaves.
