Pre-heat the oven to 180C/350F/Gas 4. Grease a 20cm round cake tin.
Measure all of the cake ingredients into a bowl and mix well until thouroughly blended and smooth. Turn into the cake tin and level.
Bake for about 50-60 minutes until the cake is well risen and shrinking away from the sides of the tin. Allow to cool. Turn out and leave to cool further.
For the topping measure all of the ingredients into a bowl and mix well until smooth. Spread over the top of the cake.