3/4 c. butter
1 c. sugar
1 egg
1 tsp. vanilla
1/4 c. milk
2 c. sifted flour
1 1/2 tsp. baking powder
1/2 tsp. baking soda
1/2 tsp. salt
3/4 c. cocoa

Cream together butter and sugar until light and fluffy. Beat in egg. Add sifted dry ingredients alternately with milk. Form into 2 or 3 rolls. Wrap in wax paper. Chill until firm in freezer. Cut into 1/8" slices. Bake on greased baking sheets about 10 minutes at 325 degrees. Remove immediately, cool on racks. Put together sandwich style with mint filling:

3 c. powdered sugar
3 or 4 tbsp. cream
About 4 drops green food coloring
1/4 tsp. salt
1/4 tsp. mint extract