Preheat oven to 350 degrees F (175 degrees C).
Sift flour and 1/4 cup confectioners' sugar together into a bowl. Rub the shortening into the flour until completely incorporated to form a dough. Roll out on a floured surface to 1/4-inch thick, then cut into 1 to 1 1/2-inch circles with a small, round cookie cutter. Place circles onto an ungreased baking sheet, and poke each twice with a fork.
Bake in preheated oven for 15 minutes. Disks should be removed from the oven while still pale, they should not brown. Cool completely on a wire rack.
To assemble the alfajores, spread one of the disks with a teaspoon of dulce de leche, then place a second disk on top, creating a sandwich. Repeat with remaining disks, then dust with confectioners' sugar.