1 c. milk
1 tbsp. vinegar
1/2 c. butter
2 c. flour
2 egg yolks
4 tbsp. cocoa
1 c. sugar
1 tsp. baking soda
1 tsp. salt
1 tsp. vanilla
1 tsp. baking powder

FILLING:

2 egg whites
2/ c. powdered sugar
3/4 c. shortening
1 tsp. vanilla

Combine milk and vinegar; let set 3 minutes. Mix together all ingredients; drop from teaspoon onto greased cookie sheet. Bake at 350 degrees for 10 minutes; let cool.

For filling, beat egg whites; add remaining ingredients and spread. Prepare filling. Spread over cooled cookie; place another cookie on top.