Add the yams to a large pot and cover with cold water. Bring to a boil, then reduce the heat to a simmer
and cook until the yams are slightly underdone, about 15 minutes. Drain
with a colander
and return the yams to the pot. Add the sugar, margarine, nutmeg and vanilla and stir together, being careful not to break up the yams
too much. Cook over medium heat until the sugar
and margarine begin to take on a syrupy consistency and the yams are cooked through, about 20 minutes. Transfer to a serving bowl.