I have done this four or five times now and can't believe how moist it keeps the lamb when you are broiling it.
The photo above shows my first experiment. Just a little goes a long way. Only 1 teaspoon of mayo is needed per side.
We made a rack last Sunday when David came over to watch the football playoffs and it worked well again.
Salt and pepper the meat well. Then smear a tsp. of mayo on each side. Sprinkle some dried mustard on top. Or mix some Dijon mustard with the may before you spread it.
The cooking time for the lamb depends on how far away your meat is from the broiler. For us, it took about 5 minutes on each side.
Instant meat thermometers come in handy for cooking lamb.
120 degrees for rare, 140 for medium . Let the meat rest for 10 - 15 minutes. It will continue to cook, especially if you tent it with a piece foil.
I don't know why it works but my theory is that the egg in mayo provides an effective barrier to keep the juices in (like a egg wash is used on pie crust) while having enough fat to brown and create a crust. At least that was my thinking when I first decided to try it.