Creme de Menthe Squares

In saucepan combine 1/2 c. of the butter or margarine and the cocoa powder. Heat and stir till well blended. Remove from heat; add 1/2 c. of the powdered sugar, the egg, and vanilla. Stir in graham cracker crumbs. Mix well. Press into the bottom of an ungreased 13x9x2-inch baking pan. Melt another 1/2 c. of the butter. In small mixer bowl combine melted butter and creme de menthe. At low speed of mixer beat in the remaining 3 c. of powdered sugar till smooth. Spread over the chocolate layer. Chill 1 hour. In small saucepan combine the remaining 1/4 c. butter and chocolate pieces. Cook and stir over low heat till melted. Spread over mint layer. Chill 1 to 2 hours. Cut in small squares. Store in refrigerator.