In fairness to your butcher, Larry, it's not a very popular cut and it also goes by a number of names: hanging tender, butcher's steak, butcher's tender, onglet, bistro steak, etc. I like the Italian and Spanish names: lombatello and solomillo de pulmon, respectively.
Most of the time I believe it's chopped up to make hamburger. I have a good friend who's a butcher at a pretty good shop nearby who claims it's a cut for the buthcer "to take home". I'm not entirely sure where it comes from -- he says it's a part of the diaphragm between the last rib and the tenderloin, near the kidney.
Grainy, and some people say it has to be marinated. I'm not so sure anymore.
Sam (the butcher) has been setting some aside for me over the past several months, and I've been learning how to cut and cook it. At first, it seemed impossibly tough, but then I learned to cut out the membrane in the middle, leaving a bit of meat on each side of the membrane
That way, Janet and I each get about four ounces of really tender meat, and Clive is delighted with his portion. Very intensely flavored, and no need to marinate.
How do you prepare yours?