Start with your leg of lamb. Mine was 7 pounds and semi-boneless, which basically meant the hip bone and socket had already been separated and the extra piece removed. You can see the exposed hip bone in the upper center of the cut part here.
Get used to working with the meat by cutting off any excess fat, especially on the skin side of the meat. This helps reduce any gamey flavors. I ended up removing at least half a pound of fat.
Carefully cut around the exposed hip bone with the tip of your (freshly sharpened) knife, separating it from the surrounding meat and tendons.
Cut along both sides of the bone on both ends, beginning to free it from the surrounding meat while at the same time keeping the meat in a single piece.
Turn the whole thing over and cut along the bottom side of the bone (hoof end), pulling the meat back from the bone on the bottom half.
Repeat on the other end (near the hip joint).
Eventually you will be able to cut the bone free from a single piece of meat. Don't forget to freeze the bone for making broth or stew.
Make a few more cuts to open up the thickest parts, and there you have it: a butterflied leg of lamb!
Spread with your delicious artichoke/bacon/Parmesan concoction (prepared the day before).
Roll the whole thing up.
Tie with kitchen string so it all stays together and looks fancy.
Roast; remove string; plop on a platter. Ooh and aah.
Carve at the table. Or let your husband do it. Whatever.