Cream butter; add sugar and beat until fluffy.
Add egg and egg yolks one at a time, beating well. Beat in vanilla and lemon rind.
Sift together cornstarch, flour, baking powder, and salt. Add to batter and mix well.
Drop batter by small spoonfuls onto well-buttered baking sheet.
Bake at 350°F for 15 minutes. Remove immediately and cool.
Sandwich the cookies together with dulce de leche.