Method
How to Make Dulce De Leche Filled Shortbread Cookies
Preheat your oven to 350°F (175°C) and prepare a baking sheet by lining it with parchment paper.
Cream together the unsalted butter and confectioners sugar in a large bowl until light and fluffy, about 3-5 minutes. Mix in the vanilla extract.
Whisk together the all-purpose flour and salt in a separate bowl. Gradually add to the butter mixture until just combined.
Shape the dough into a disk, wrap in plastic wrap, and refrigerate for 30 minutes.
Roll out the chilled dough to about 1/4-inch thickness on a lightly floured surface and cut out shapes.
Bake the cookies for 10-12 minutes until edges are barely golden. Cool completely on a wire rack.
Simmer the unopened can of sweetened condensed milk in a pot of water for 2-3 hours. Open can to reveal dulce de leche.
Mix in a pinch of kosher salt to the dulce de leche, then spread onto half of the cooled cookies. Top with other half to create sandwich cookies.
Dust with confectioners' sugar if desired.
Notes
Ensure butter is at room temperature for easier mixing. Do not overmix the dough after adding flour to keep cookies tender. Simmer the milk fully submerged to prevent uneven cooking.