Preheat the oven to 180'C.
Melt the chocolate in a heatproof bowl over simmering water (bain-marie).
Sift the flour, baking powder and cocoa powder together. In a bowl, beat the sugar and the butter together until the mixture is pale and fluffy. Beat the eggs into the butter mix one at a time. Gently fold in the flour mix and then add the white chocolate buttons. Next fold in the melted chocolate.
Pour the mixture into a cake tin and bake for 30 to 40 minutes. After about 30 minutes check the cake is cooked by inserting a skewer into the centre. If it comes clean it is ready. Allow to cool and then transfer to a cooling rack or plate to ice the top of the cake.
Melt the white chocolate with the cream over a bain-marie. Whisk the oil in to the mix until you have a smooth liquid. Allow to cool slightly and then pour over the cake.
«The chocolate icing should be cold enough before pouring over the cake but still runny. The consistency should be of a thick batter.»