Step 1: Prepare Dulce De Leche

To make Dulce de Leche, add milk, granulated white sugar, light corn syrup, baking soda and salt in a large saucepan. Place saucepan over high heat and bring milk just to a boil. Watch carefully and as soon as the mixture begins to foam up, stir it with a heatproof spatula and reduce heat to medium until the mixture is just at a low rolling boil. Continue to cook the mixture, stirring the bottom and sides of the saucepan frequently, until the mixture becomes very thick, sticky and caramel colored. Remove Dulce de Leche from heat and stir in the vanilla extract and leave it for cool completely.

Step 2: Prepare Alfajores Dough

To make alfajores dough, in a large bowl combine cornstarch, flour, baking powder, salt and stir it well. Add butter and blend into the flour mixture with a pastry blender or with your hands. Add powdered sugar, vanilla extract and knead it into smooth dough with your hands.

Step 3: Shape and Bake The Cookies

To shape and bake the cookies, preheat the oven at 350 degrees. Sprinkle flour on the cutting board. Roll the dough into 3/8 inch thick in size. Then cut the dough into 2 inch circles with cookie cutter. Place dough circles on a prepared baking sheet. Place cookies in the oven and cook for 15 minutes until light golden color.

Remove cookies from the oven and allow it to cool for 5 minutes. Then transfer cookies onto wire rack to cool completely.

Step 4: Assemble and Serve Alfajores

To assemble and serve alfajores, add Dulce de Leche to one cookie and then top it with another cookie to make a sandwich. Repeat same process for all the cookies. Sprinkle powdered sugar on the top of alfajores. Your Alfajores are ready to serve.