Cream butter and sugar until light and fluffy. Add egg yolks and vanilla, mix well.

Whisk flour, cornstarch, baking powder, and salt. Gradually combine with butter mixture to form dough.

Chill dough for 15–20 minutes.

Preheat oven to 350°F (175°C). Roll dough to 1/4-inch thickness and cut hearts. Place on parchment-lined baking sheet.

Bake 8–10 minutes until edges are lightly golden. Cool completely on wire rack.

Spread 1 tsp dulce de leche on one cookie and sandwich with another.

Dust with powdered sugar before serving.