Mary Berry’s red velvet sandwich cake

Butter, for greasing

250g (9oz) plain flour

1 tbsp cocoa powder

2 tsp baking powder

1 tsp bicarbonate of soda

250g (9oz) light muscovado sugar

200ml (⅓ pint) buttermilk

150ml (¼ pint) sunflower oil

2 tsp vanilla extract

1 tbsp red food colouring gel or about ¼ tsp food colouring paste

2 large eggs

8 white chocolate truffle balls, to decorate

For the buttercream icing:

250g (9oz) butter, softened

2 tsp vanilla extract

300g (10½oz) icing sugar

250g (9oz) full-fat mascarpone cheese