225g (8oz) margarine
225g (8oz) caster sugar (I cut down to 180g)
275g (10oz) self-raising flour
2 level tsp baking powder
4 large eggs
2 tbsp milk
½ tsp vanilla extract
1½ level tbsp cocoa powder
2 tbsp hot water
For the icing
25g (1oz) butter
15g (½oz) cocoa powder, sifted
1-2 tbsp milk
100g (3½oz) icing sugar, sifted
about 25g (1oz) white chocolate, melted
1) Preheat the oven to 160°C/Fan 140°C/gas 3. Lightly grease a 900g (2lb) loaf tin, 17 x 9 x 9cm (6½ x 3½ x 3½in) base measurement (I used a 9”x5” loaf pan) and line with a wide strip of non-stick baking parchment to go up the wide sides and over the base of the tin.
2) Measure (A) into a large bowl and beat with a hand-held electric mixer for about 2 minutes, until well blended. Spoon half the mixture into another bowl and set aside.
3) In a small bowl, mix the cocoa powder and hot water together until smooth (I prepared this first before step 1). Allow to cool slightly, then add to one of the bowls of cake mixture, mixing well until evenly blended.
4) Spoon the vanilla and chocolate cake mixtures randomly into the prepared tin until all of the mixture is used up, and gently level the surface. Bake for 50 minutes to 1 hour, until the cake is well risen, springy to the touch and beginning to shrink away from the sides of the tin. Allow to cool in the tin for a few minutes, then turn out onto a wire rack, peel off the lining paper and leave to cool completely.
To make the icing, melt the butter in a small pan, add the cocoa powder, stir to blend and cook gently for one minute. Stir in the milk and icing sugar, then remove from the heat and mix thoroughly. If necessary, leave the icing on one side, stirring occasionally, to thicken. Spread the cold cake evenly with the icing, then drizzle the melted white chocolate over the top. Leave to set.