In a large bowl, cream butter and confectioners' sugar until light and fluffy. Add vanilla. Combine flour and cornstarch; gradually add to creamed mixture and mix well.
Roll into 3/4-in. balls. Place 1 in. apart on ungreased baking sheets. With fingers, flatten to 1/4-in. thickness, forming eye shapes. For variety, shape some balls into logs, then flatten. Bake at 350° for 9-10 minutes or until edges begin to brown. Remove to wire racks to cool.
For frosting, in a small bowl, beat butter and confectioners' sugar until smooth. Add enough lemon juice to achieve a spreading consistency. Beat in lemon zest. Tint frosting purple and/or neon green; frost cookies. Add kisses for pupils.