Sift the cornstarch, plain flour, and baking powder into the bowl and gently fold it in with a spatula. Then knead by hand, and make into a ball.
To make prettier looking alafajores, you would need to use Dulce de Leche Repostero, which is thicker than regular Dulce de Leche. This way, your Dulce de Leche will be more stable and it will not look as messy as mine. To make Dulce de Leche Repostero, you can add 1 tablespoon of cornstarch dissolved into 4 tablespoons of milk to your Dulce de Leche when you make it (towards the end of the cooking process).