In a medium saucepan saute shallots in butter until golden, about 3 to 4 minutes. Add the sweet potato and couscous and continue cooking for 2 more minutes or until they are both golden. Add the stock and spices and bring to a boil. Cover and reduce to low heat. Simmer for about 12 minutes or until liquid is absorbed. Remove from heat and let stand for 5 minutes. Fluff with fork and serve with lamb.