Step 1

Preheat oven to 350 degrees F.

Step 2

Combine garlic, olive oil, rosemary, thyme, mustard, salt, and pepper in a bowl. Rub all over the leg of lamb.

Step 3

Drizzle the potatoes with olive oil, then sprinkle with salt and pepper and place in the bottom of a casserole dish or roasting pan. Place the leg of lamb on top.

Step 4

Roast for 1 1/2 to 2 hours (longer if using bone-in) until you reach medium-rare, which is 130-135 degrees F on a digital meat thermometer inserted into the center of the lamb.

Step 5

Remove from oven and let the lamb rest for 15 minutes before slicing and serving.