Ok, new cut of meat, for me: what they called Easy-carve leg of lamb, which is boneless on top but not bottom.

Day 1: Put a lot each of that peeled garlic I love, whole white peppercorns, and rosemary, and a little each of grosgrain mustard and olive oil, into a food processor, made mush.
Untied the leg, opened that end up, crammed every nook and slathered the outside with the mush, wrapped the leg tightly in parchment paper. Put in fridge.
Day 2: brought leg to room temp. Unwrapped, rewrapped the meat around the boneless end, retied it tightly. Put leg in roasting pan. To keep the mush that was falling off from burning, put some white wine in bottom of roasting pan. Just before sticking into preheated 450 oven, poured a little garlic oil onto the top, rubbed that in. Hot oven 15 mn, then 350 for an hour. Let sit out of oven while deglazing roasting pan, finishing any accompaniements, and so on. Pour deglazed juices into separator.
It made a marvy crust. Marvy juices. The lamb was perfectly rare -in fact, I wouldn't have minded another 15 mn, but I took the edge piece.

Success at first leg!