Preheat oven to 170°C (340°F) and line a baking tray with parchment paper.
In a bowl, cream butter and powdered sugar until light and fluffy.
Add vanilla extract and mix well.
Sift in flour, cornstarch, and salt, then combine to form a soft dough.
Roll out the dough and cut into equal-sized round cookies.
Place on the tray and bake for 12–15 minutes until lightly golden at the edges.
Let cookies cool completely.
Spread dulce de leche on one cookie and sandwich with another. Serve and enjoy.