Preheat the oven to 350°F. To make the pastry, mix the flour with the butter, confectioner's sugar and the lemon zest. Gently knead until mixture forms mass. Divide pastry in three pieces. Roll out on lightly floured surface. Cut a circle of about 11 inches. Place the pastry, on a previously greased and lined baking pan. Bake for 15 to 20 minutes. Allow to cool. Roll out remaining pastry following the steps above. Once the 3 layers are baked, spread bottom layer manjar blanco. Add the second layer and spread with manjar blanco. Place the third layer and dust with confectioner's sugar.
Optional: You can also make alfajores of 1 inch each.To make the filling, place the cans of condensed milk in a large saucepan, the water should cover the cans. Boil for two hours or 45 minutes in a pressure cooker. Cool in iced water before opening.