Creamy, confectionery dulce de leche is sandwiched between buttery cake-like cookies in this sweet traditional South American treat. Method 1. Combine cornstarch, flour, baking powder, baking soda, and salt. Set aside. 2. Using a stand mixer beat butter and sugar until light and fluffy. Add egg yolks, Pisco and vanilla, mix. 3. On low speed, gradually add flour mixture until incorporated with no visible white pockets. 4. Shape dough into a smooth disk, wrap in plastic. Refrigerate 1 hr. 5.