Sift flour and baking powder.
Whip butter with sugar until creamy and fluffy. Add egg yolks, one by one, while beating. Add sifted ingredients and lemon peel.
Place mixture on a horizontal surface and knead with hands, forming a ball. Cover with a cloth and set aside for 20 minutes. If mixture seems too dry, add more milk. Flour the surface generously and roll dough to 1/8 inches (3 mm) thick approximately. Cut circles (2 ½ inches / 5 cm).
Transfer them to a greased and floured cookie sheet.
Bake in preheated oven 350° F (175° C) for 30 minutes or until edges begin to color..
Remove from oven. Allow to cool.
Take one cookie and generously spread manjarblanco. Cover with another cookie.
Yields: 20 alfajores