Beat 4 eggs for 5 minutes with a whisk and mix them with the powdered sugar, beating until creamy. Set aside.
Sift together the cornstarch, the flour, and the baking powder.
Pour out onto table top; in a well in the centre, place the butter at room temperature, the vanilla extract, the liquer and the egg and sugar cream.
Work with your hands until firm.
Roll with a rolling pin to a thinkness of 1 1/4 inch and cut into 1 1/2 inch discs with a cookie cutter. Place the discs on a greased and floured cookie sheet.
Bake for 20 to 25 minutes at medium (350F), until golden. Remove and cool.
To put together each alfajor, spread a 1/4-inch coat of dulce de leche over one disc, cover with another, paint the edge with a little more dulce de leche and roll it on the grated coconut so that it sticks to the edge.
HOMEMADE DULCE DE LECHE:.
Heat 8 tablespoons of sugar in a thick bottomed pot for 20 minutes at medium, until it reaches a caramel color.
Add the milk and the remaining sugar and allow to reach a boiling point.
Bring the heat to minimum, and simmer until it thickens, for about an hour.
HOMEMADE DULCE DE LECHE - EASY VERSION.
Boil an unopened can of condensed milk for two hours in a saucepan filled with water. When you open it, its contents should have a rich caramel color.