Beat I Can't Believe It's Not Butter!® Spread with sugar in large bowl with electric mixer until light and fluffy, about 2 minutes. Beat in egg yolk and vanilla. Beat in flour until blended.
Shape dough into one log, about 12 x 1-1/2-inches. Wrap in plastic wrap and refrigerate at least 1 hour. (May be stored in refrigerator up to 3 days or in freezer up to 2 months.)
Preheat oven to 350°. Slice dough into 1/4-inch slices and arrange on ungreased cookie sheet.
Bake 12 minutes or until lightly golden around bottom edges. Cool completely on wire rack. Drizzle with or dip in melted chocolate, if desired.
NOTE: May be sliced and baked as needed directly from the freezer. Bake as above.
Makes 4 dozen cookies