Cream together the butter and the sugar until light and fluffy. Gradually blend in the custard powder and the flour. Using an icing bag fitted with a large star nozzle, pipe out -10ºC ingers, well apart, on to greased baking sheets. Bake at 180ºC ., 180 degrees C., Gas Mark 4, for 20 minutes. Leave to cool on a wire rack. Melt the chocolate in a bowl over a pan of hot water. Dip both ends of the Viennese Fingers into the melted chocolate and leave until set. ----