Preheat oven to 500 degrees. Prepare a 9x13 roasting pan by spreading light extra virgin olive oil in the bottom and then laying springs of fresh herbs on the center, a nice bed of aromatics for your leg of lamb to rest on while it roasts.
Place boneless leg of lamb on a clean work surface, like a cutting board. Pierce the top with a knife, making slits deep enough for garlic slices. Fill the slits with garlic. Next, rub the surface with coarse sea salt and pepper. Slather with Dijon mustard and finally press fresh, chopped rosemary and thyme into the Dijon mustard. Transfer boneless leg of lamb to the prepared roasting dish.
Place into the hot oven for 20 minutes. This will create a nice crust and seal in juices.
After 20 minutes, lower heat to 350 degrees. Open oven door to allow excess heat to escape and cool down the oven fast. Continue to roast for 40-60 minutes. Time will vary greatly depending on size of your leg of lamb and your preferred level of doneness.
Remove roast after reaching desired temperature. Allow to rest for 15 minutes before carving. Carve against the grain and serve with a side of mint jelly.
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Notes
Easily chop fresh herbs using kitchen shears or a mini food processor. *You can use this recipe with a bone-in leg of lamb as well.