Sift flour once, measure, add cocoa, baking powder and salt and sift together three times. Cream butter thoroughly, add sugar gradually, and cream together until light and fluffy; then beat in egg. Add flour, alternately with coffee, a small amount at a time, beating after each addition until smooth. Add vanilla. Bake in two greased 23 cm layer pans in moderate oven, 190ºC 30 minutes. Cool. Add confectioners' sugar to whipped cream, mixing until blended. Fold dates and nut meats into whipped cream. Spread between layers of cake. Sift confectioners' sugar over top of cake.