2 ½ cups all-purpose flour, or as needed
2 ½ cups cornstarch, or as needed
½ teaspoon baking powder
2 cups butter, softened
2 eggs plus 2 yolks
2 tablespoons Malibu rum
1 teaspoon vanilla
Grated zest of 1 lemon
Dulce de Leche
Makes about 16 sandwich cookies
Stir the flour, cornstarch, baking powder and salt together in a large bowl until well blended. Beat the butter and sugar together in the bowl of an electric mixer fitted with the whisk (or in a bowl using a handheld mixer) at high speed until pale yellow and fluffy. Beat in the Malibu, vanilla and lemon zest one at a time. Switch to the paddle attachment (or a wooden spoon if you’re using a handheld mixer), add 2 ½ cups each of the flour and cornstarch and mix at low speed just until incorporated.
The dough should form a soft ball, but not be sticky or runny. If necessary, add a little bit of each the flour and cornstarch and mix.
Chill the dough until firm, at least 1 hour or up to 1 day. Let the dough stand at room temperature 15 minutes before continuing.
Preheat oven to 350° F Divide the dough in half and roll each half out on a lightly floured surface to about ¼ inch thick. Cut into 3-inch circles and line up on a greased or non-stick baking sheet. Work in batches or use multiple baking sheets. Bake until the cookies are pale golden brown, about 12 minutes. Rotate the pans from shelf to shelf and front to back once as the cookies bake. Cool completely.
Using 2 cookies and about 1 tablespoon of the sweetened milk treat as filling, make sandwiches. The cookies will keep at room temperature for up to 3 days.
For decoration, press the cookie sandwiches lightly so the filling oozes out just a tad. Set out plates with different “toppings” like shredded coconut, salted peanuts, or cocoa powder and have your guests Roll the edges in shredded coconut (toasted if you like), chopped salted peanuts or cocoa powder.