Mix salt, black pepper, brown sugar, thyme, onion powder and cayenne together in a small bowl. Rub pork chops with the spice mixture. Wrap and place in refrigerator for a few hours.
Set up your grill/smoker for indirect heat at 275 degrees F., using charcoal and add a handful of the soaked apple wood chips onto the coals.
Place pork chops on the grill. Close grill and maintain a temperature of 275 degrees F, adding more charcoal and chips, as necessary. Let smoke for 1 hour and 10 minutes, until the pork chops are firm to the touch. Transfer to serving plates and serve with the BBQ sauce.
Buttermilk BBQ Sauce:
In a medium saucepan over medium-low heat, add the apple cider and brown sugar and stir to combine. Allow to reduce for 25 minutes. Reduce the heat to low, pour in the BBQ sauce and stir well. Once sauce has warmed, turn off the heat. Add buttermilk and stir to incorporate. Serve over pork chops.