We have been cooking butterflied leg of lamb for more than 20 years -- mostly following Julia Child's recipe where you marinate in olive oil, garlic, lemon, etc. and grill or cook in the oven. For most of that time I had to deal with taking out the bone as part of the process. Of course after Costco arrived, I got spoiled and it's already butterflied when I buy it. Which is nice.
Tuning around I happened on America's Test Kitchen and they did a recipe that knocked my socks off. I knew I had to make it some day and I joined the site just so I could print out the recipe. You butterfly and then you cut "accordion" slits in the non-fat side (same as Julia) but you also pound it down to about an even inch thick throughout. And then you cut a checkered pattern in the fat and rub that side with salt for broiling. But the coolest thing was the first step.
You combine a tablespoon each of mustard seed, cumin seed, and coriander seed with 3 bay leaves and 1/3 cup of olive oil. You thinly slice 3 shallots and stir those in, and mash 4 garlic cloves and stir them in. Add 2 two inch strips of lemon zest (use a peeler). You stir this mixture and then spread it out on a rimmed cookie sheet, in the approximate shape of the lamb. Bake in a 250 degree oven for about an hour (I thought it was done after 45 minutes).
Meanwhile the salted lamb was lying under wax paper and cookbooks getting flatter. After the cookie sheet comes out of the oven (smells really good) you give it a last arranging stir and then put the lamb on top, meat side down. Put back in the 250 oven and roast until the meat hits 120 degrees. Take it out and set the oven on Broil. When it's hot, put the meat back in on a high shelf until the top browns. BTW after baking/roasting for 20-25 minutes the meat looks kinda sad and gray. If I hadn't seen the transformation from the broiling step on TV I might have been discouraged at this point. But look at the picture:https://www.americastestkitchen.com/rec ... tard-seeds