Like marshmallow Peeps, the butter lamb is another Easter icon. Lambs are symbols of the Lamb of God, the resurrection of Jesus, and are part of the Polish Easter tradition. But plenty of people just buy them for their good looks. Butter lambs are usually made by hand or in a mold. For those not up to the chore, pre-made butter lambs are for sale in some grocery stores, produced by Keller's Creamery. We found this lamb chillin' in the dairy case at the Met Foods in Prospect Heights, Brooklyn. Look for lambs now . . . butter turkey and butter Christmas trees will follow in November and December. Serving a Margarine Lamb, complete with raisin hooves and peppercorn eyes, would probably make you the black sheep of the family.