Brush the pork chops with oil, rub in the spice mixture and then place in a shallow dish. Leave to marinate in a cool place for 2 hours.
Meanwhile, beat the butter, tarragon and some pepper together until well blended. Roll into a log and wrap in clingfilm, then chill until required.
Cook the steaks on a hot barbecue for 4—5 minutes on each side, then wrap loosely in foil and set aside to rest for 5 minutes. Cut the butter into slices and serve on top of the steaks, with lemon wedges alongside.