Mix butter, flour and sugar. Blend with a fork or a pastry blender.
Finish kneading with hands until a uniform dough is obtained. If needed, add a few sprinkles of water as needed to make dough easy to roll.
Roll dough on a flour surface. Cut circles with a round cookie cutter (the size and form are optional).
Transfer them carefully to greased cookie sheet.
Bake in preheated oven 350° F (175° C) for 12 to 15 minutes. Remove from oven. Cool.
To assemble: take one of the cookies, and carefully spread with manjarblanco. Cover with another cookie. Sprinkle with sifted confectioners sugar.
*Something very similar to manjarblanco can be found in many US grocery stores under the Nestle label called Dulce de Leche (read carefully, there are similar sounding names that will not give the same result).
**For larger cookies, double the recipe, and make 10-inch circles (25 cm). It is better to roll the dough on top of a plastic film or parchment paper. This way it will be easier to transport. Once on the cookie sheet, remove film or paper. Yields: 3 circles.
Proceed as with the small alfajores.
Yields: 60 alfajores (2 inches - 4 cm)