Remove fell (thin outer coating) from lamb. Combine melted butter, lemon juice, parsley & mint; add garlic that has been mashed with salt, pepper & sugar. Heat, stirring constantly, until sugar melts. Baste lamb well with sauce. Place lamb in roasting pan on rack & roast 325 oven, allowing 25 minutes per lb. If fresh; 37 minutes per lb. If frozen, basting frequently. Mash yams & whip with butter & egg. Garnish with lemon slices.