Step 1

Melt 1/2 cup butter; add one ingredient at a time, stirring after each addition: cocoa, 1/2 cup powdered sugar, egg, 2 teaspoons vanilla, graham cracker crumbs and chopped nuts. (Start with 2 1/2 cups graham cracker crumbs and add more if needed. You don't want it to be too dry.) Press into the bottom of a 13x9x2 inch pan.

Step 2

Melt 1/4 cup butter. In a small bowl, mix cornstarch and 2 teaspoons sugar; add to the melted butter and whisk until smooth. Add half and half or milk. Cook mixture over low heat, stirring constantly until thick and smooth; cool slightly.

Step 3

Add 1 teaspoon vanilla and 2 cups powdered sugar to cooled mixture; whisk until smooth and thick. Pour over the bottom layer and spread evenly with an offset spatula.

Step 4

Melt chocolate over hot water (double boiler). Spread over the cream layer. Let cool at room temperature until chocolate hardens.

Step 5

Cut into bars before the chocolate is completely set. Cut into dainty squares.