Blitz anchovies, garlic, mustard, red wine vinegar, lemon peel, stevia and 2 tablespoons olive oil to make a paste. Spread over the inside of the butterflied lamb.
Roll the lamb up on a board and tie tightly with kitchen string. Any excess paste that has come out, take and spread over the top of the lamb leg.
Drizzle with remaining olive oil and season lightly with salt and pepper. Place in a roasting dish on a rack. Pour enough water into the bottom of the dish to cover it. Roast at 180C for approximately 1 hour 20 minutes for medium.
Check occasionally and top up the water level if necessary. Don’t let it dry out. Once finished cover and set aside.
Strain liquid from roasting pan into a small pot and add cream. Simmer and reduce until thickened. Slice lamb and serve with mash, sauce drizzled over.