This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
All the slices of mutton that can be cut on both sides of the spine bone from the neck to the hip. The first choice are the rib chops, the shortened ribs giving an advantageous shape; the loin chops are even better eating; they are cut from the saddle of mutton.
Double thickness; the meat of two with but one bone.
Restaurant specialty. A sample sent to an editor who had heard of them weighing 1 1/2 lbs. "It is usual to boil them 5 minutes before placing them on the grill, as, owing to their thickness, they would otherwise be black outside before being cooked in the middle. The plan is always to have some chops ready-boiled, so that they may be grilled off as ordered, and by this means they are dished as soon as an ordinary chop - by the time the tea is made, or the chip pototoes ready for serving. Although half cooked, perhaps, the day before grilling, a Barnsley chop is still fresh cooked, has more gravy in it than the ordinary mutton chop, and is more satisfying for a hungry customer".