Melt first 3 ingredients in top of a double boiler. Add egg and stir to cook and thicken Remove from heat. Stir in crumbs, coconut and nuts. Press firmly into an ungreased 8 X 8 pan.
SECOND LAYER
Cream butter, cream, custard powder and icing sugar together well. Beat until light. Spread over bottom layer.
THIRD LAYER
Melt chocolate and butter over low heat. Cool. When cool, but still liquid, pour over second layer and chill in refrigerator.