In a mixing bowl, combine margarine, sugar, egg yolk, flour, and vanilla extract. Mix until smooth. Shape into a roll 1 1/2" thickness. Wrap in plastic wrap and chill for two hours. Preheat oven to 375. Cover two baking sheets with wax paper. Unwrap cookie dough and cut the log into 1/4" slices. Place slices one inch apart on the baking sheet. Fold two edges of each cookie over the center so that they overlap and each cookie has a point on one end and a rounded bell shape on the other. Tuck a cherry half into each cookie. Bake for ten minutes or until cookies are pale golden brown. Store in airtight container.