Spiessbraten (in Idar Oberstein where it is famous, they call it schwenkbraten, which means that it's cooked on a "swing" grill).
Pork tenderloin 3/4 inch thick (the more marbled, the better).
Liberally sprinkle cutlet seasoning, garlic salt, on the pork. (Germans use a spice called liebstockel (Known as Lovage in english), but I haven't been able to find it here in the states).
Layer between onion slices 1/4 inch thick in a sealed container (tupperware). For larger groups there can be any number of layers that will fit in your container (layer of onions, then a layer of cutlets that have been seasoned, then another layer of onions, then another layer of cutlets, lastly covered with a layer of onions.)
Turn container every 30 minutes or so..or whenever you happen to think about it. It's best to let it marinade all day, or even overnight (in the refrigerator for an overnighter) - but at least 4 hours. The juice from the onions will tenerize and flavor the meat.
Best to grill or broil meat after all this. The very best way is to cook it is on a "swing". This is a grill suspended from a tripod which cooks over the coals that you just keep moving while the pork cooks.
Americans have a phobia about undercooking pork, but this is best when it is cooked medium. Overcooking it dries it out and ruins the quality.
Serve with spazel and/or pom frites.
Being thriftful, and also liking onions, I take the spiced up onions that the meat has marinaded in, and fry them up in a little oil and butter. It looks like a big batch of fried onions, but they cook down, and they're great with the pork cutlets. I don't recall the Germans doing this, but I like it.