Preheat oven to 350 degrees F (175 degrees C). Grease baking sheets.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla.
In a separate bowl, sift together the flour, baking powder, and salt. Gradually stir the dry ingredients into the creamed mixture.
Roll the dough out onto a lightly floured surface about 1/4 inch thick. Cut out circles with a cookie cutter, and place onto the prepared baking sheets. Bake for 8 to 10 minutes in the preheated oven, or until golden.
Remove from cookie sheets to cool on wire racks. Once cooled, spread a tablespoon of dulce de leche onto half of the cookies, and top with the remaining cookies to form sandwiches.
Interesting Facts
Alfajores originated in Argentina, but are popular in many Latin American countries.
Dulce de leche is made by reducing milk and sugar over low heat.
Alfajores cookies can be filled with many different flavors, including chocolate and fruit jams.