Grease 2 round cake tins and line the bases. Cream the butter and sugar together in a bowl until they are light and fluffy.Gradually beat the egg. Preheat the oven to 180oc (350of/Gas4).Sieve the flour,cocoa powder and baking powder into the bowl and fold them into the creamed mixture.Divide the mixture equally between the 2 greased and lined cake tins, smoothing the tops with a palette knife. Bake for 20-25 mins or until firm.Turn the coocked cakes outonto a cooling rack. Break the plain and milk chocolate into a bowl and gently melt them over a pan of simmerind water. Remove the bowl from the pan. Allow the chocolate to cool for 5 mins and then stir in the cream.Leave the mixture to thiclen for a few mins. Make sure the cakes are completely cool before putting on the topping. Put one cake on a serving plate and spread a quater of the topping over it. Put the other cake on top and spoon over the rest of the topping. Spread it over the top and the sides until the cake is evenly set. Use the white chocolate and break it up and cut in half with a sharp knife. once you have done this then stick the chocolate peices into the top of thcake and leave it all to set.