Preparation Pulse garlic, parsley, fennel seeds, and 1/2 cup fennel fronds in a food processor until very finely chopped. With motor running, slowly add 1/4 cup oil and process until smooth; season generously with salt and pepper (mixture should taste quite salty as this is the only seasoning meat will get). Rub parsley mixture all over lamb. Transfer to a roasting pan, cover, and chill at least 8 hours. Let lamb sit at room temperature 1 hour. Bring vinegar and honey to a boil in a small saucepan. Reduce heat and simmer, stirring occasionally, until slightly thickened, 8–10 minutes. Set glaze aside. Place racks in lower third and middle of oven and preheat to 325°F. Toss fennel and carrots with remaining 1/4 cup oil in a medium bowl and arrange half around lamb in roasting pan; place remaining vegetables on a rimmed baking sheet. Roast vegetables on baking sheet on lower rack and lamb on middle rack until an instant-read thermometer inserted into the thickest part of lamb registers 100°F, about 1 hour. Increase oven to 450°F, brush roast with glaze, and continue to roast until an instant-read thermometer registers 120°F, 20–25 minutes longer. Transfer lamb to a cutting board and let rest 30 minutes before carving (temperature will rise to 140°F for medium-rare while lamb is resting). Continue to roast vegetables, tossing occasionally, until golden and tender, 20–25 minutes longer. Serve lamb with vegetables, topped with fennel fronds. DO AHEAD: Lamb can be rubbed with parsley mixture and vegetables can be prepped 1 day ahead. Cover separately and chill. Slice it rightCarving a leg of lamb is easier than you think. Here's how to do it with flair. 1. Position the roast so that the meatier side faces down. Using a long, thin-bladed knife and holding the end of the shank bone, remove a few strips of meat from the top side, working parallel to the bone. 2. Rest the leg on the flat area you just created. Cut thin slices perpendicular and all the way down to the bone, starting at the end farther away from you. 3. Starting at the top and working away from your body, slide the knife underneath the slices you just made. Remove in one long sawing motion. 4. Rotate the bone and repeat with the less meaty side; trim any remaining meat from the sides of the bone.
Preparation Pulse garlic, parsley, fennel seeds, and 1/2 cup fennel fronds in a food processor until very finely chopped. With motor running, slowly add 1/4 cup oil and process until smooth; season generously with salt and pepper (mixture should taste quite salty as this is the only seasoning meat will get). Rub parsley mixture all over lamb. Transfer to a roasting pan, cover, and chill at least 8 hours. Let lamb sit at room temperature 1 hour. Bring vinegar and honey to a boil in a small saucepan. Reduce heat and simmer, stirring occasionally, until slightly thickened, 8–10 minutes. Set glaze aside. Place racks in lower third and middle of oven and preheat to 325°F. Toss fennel and carrots with remaining 1/4 cup oil in a medium bowl and arrange half around lamb in roasting pan; place remaining vegetables on a rimmed baking sheet. Roast vegetables on baking sheet on lower rack and lamb on middle rack until an instant-read thermometer inserted into the thickest part of lamb registers 100°F, about 1 hour. Increase oven to 450°F, brush roast with glaze, and continue to roast until an instant-read thermometer registers 120°F, 20–25 minutes longer. Transfer lamb to a cutting board and let rest 30 minutes before carving (temperature will rise to 140°F for medium-rare while lamb is resting). Continue to roast vegetables, tossing occasionally, until golden and tender, 20–25 minutes longer. Serve lamb with vegetables, topped with fennel fronds. DO AHEAD: Lamb can be rubbed with parsley mixture and vegetables can be prepped 1 day ahead. Cover separately and chill. Slice it rightCarving a leg of lamb is easier than you think. Here's how to do it with flair. 1. Position the roast so that the meatier side faces down. Using a long, thin-bladed knife and holding the end of the shank bone, remove a few strips of meat from the top side, working parallel to the bone. 2. Rest the leg on the flat area you just created. Cut thin slices perpendicular and all the way down to the bone, starting at the end farther away from you. 3. Starting at the top and working away from your body, slide the knife underneath the slices you just made. Remove in one long sawing motion. 4. Rotate the bone and repeat with the less meaty side; trim any remaining meat from the sides of the bone.