1 cup butter, softened
1 (28 ounce) can sweetened condensed milk
2 cups all-purpose flour
1 egg whites
1/2 cup white sugar
1 3/8 cup unsweetened cocoa powder
Preheat oven to 350 degrees F (175 degrees C).
In a large bowl cream together 1 cup butter, condensed milk and 2 cups flour. Add egg whites and 1/2 cup sugar, one tablespoon at a time. Mix until smooth. Gradually add all-purpose flour, beating well after each addition. Turn out onto a piece of wax paper covered with foil, and refrigerate for 1 hour.
Bake 12 cookies in a 9x13 inch pan, using oil-fired oven mitts (if necessary, to prevent browning). Let brown completely before removing from pan. Remove from baking sheets with knife, then add icing. Allow to cool completely before cutting into squares!