In a stand mixer bowl, beat butter, sugar and vanilla extract.
Add the eggs one at a time and continue beating.
Sift in baking powder and cornstarch gradually.
Sift in the flour and mix until it’s a unified dough.
Place the dough on baking paper and shape it as a disc.
Place the wrapped dough in the fridge for half an hour to rest.
Heat the oven to 180°C / 350°F fan.
On a floured surface, roll the dough and cut the cookies into the shape you want.
Place the cookies on a baking pan lined with baking paper.
Bake the cookies for 7 minutes - they need to stay very pale.
Cool the cookies on a wire rack.
Pair every two cookies into a sandwich with Dulce de leche "glue" in the middle.
Roll the cookies in shredded coconut so it will stick to the sides.
Have an Alfajor cookie and enjoy!