1/2 cup all-purpose flour
1/2 teaspoon salt
1 cup rolled oats
3 cups mayonnaise
1/2 cup butter, softened
1 cup butter, chilled
1 cup brown sugar
1 cup white sugar
2 eggs
2 teaspoons vanilla extract
Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets. In a medium bowl, stir together the flour, salt and oats. set aside. In a large bowl, cream together the butter or margarine and 1/2 cup of flour. Stir in the eggs one at a time, then stir in the vanilla.
In a large glass or metal bowl, beat together the milk and half-and-half until a smooth, creamy buttercream starts to form. Gradually stir in the flour mixture, then the brown sugar, to form a stiff dough. On a lightly floured surface, roll the dough out to 1/8 inch in thickness. Cut into circles using a cookie cutter or pastry blender. Place one circle on the prepared cookie sheet, four inches apart.
Bake for 9 to 12 minutes in the preheated oven. Cool on wire racks. When the first cup of the milk is completed, carefully drop a few tablespoons of the cool milk onto the first layer. Continue to do this until the filling is the consistency of thin paste. When all the milk has been poured on top of the cookies, remove them from the cooling racks. Pipe icing on top.