Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch round cake tin.
Lightly grease and dust the cake tin with flour. Sift together the flour, carob powder and baking powder. Add the sugar and mix well.
As quickly as possible, add the oil, malt extract, vanilla essence and warm water to the bowl and beat together until well combined. Pour the mixture into the prepared tin. Smooth the top and make a slight hollow in the centre, to prevent splits forming. Bake in the middle of the oven for about 40 minutes. Test with a warm knife. Allow to cool before removing from tin.
Cream all the topping ingredients together until thick and smooth. Spread evenly over the cake and smooth out any imperfections using a cake slice dipped in cold water.