7 cups chicken, or vegetable stock
2 pounds fresh carrots, peeled
3 leeks, sliced in half lengthwise and thoroughly cleaned
1 yam, peeled
4 stalks celery
4 tablespoons butter
1 (3-inch) piece fresh ginger root, peeled and grated
1 teaspoon ground nutmeg
1 teaspoon salt
1 teaspoon freshly ground black pepper
1/2 pint heavy cream (optional)