METHOD
1. You’ll need two 18 or 19cm round cake tins, buttered, floured and lined with a disc of parchment at the bottom. Preheat the oven to 175C/350F/gas 4.
2. Sift together the flour, cocoa and salt into a bowl. In another bowl or the bowl of a standing mixer, beat the butter with the sugar until fluffy. Add the eggs, one at a time, scrape the sides of the bowl as needed, add the vanilla extract and beat until combined.
3. Stir the red colouring into the buttermilk. Add to the butter mix alternating it with the flour, in three goes, beginning and ending with the flour.
4. Mix the bicarb of soda with the vinegar in a small cup, let it fizz and fold it quickly into the batter.
5. Divide the batter between the two tins, smooth the surface and bake for 25-30 minutes until a skewer inserted in the middle comes out clean. Cool the cakes in the tins on a wire rack for 10 minutes. Place a wire rack on top of the cake tin and invert, lifting off the tin. Once the cakes have completely cooled, wrap them in plastic and place in the fridge for at least an hour, or overnight.
6. To make the frosting, beat the cream cheese with the mascarpone until smooth, using an electric mixer or a hand whisk. Beat in the icing sugar and the vanilla. Beat or whisk in the cream until the frosting thickens and reaches spreading consistency.
7. To assemble, slice each cake horizontally in two. ( If you want to decorate it with cake crumbs, trim the sides of one or both cakes, slice off uneven top of one or both or sacrifice one cake layer. Dry the trimmings in a medium oven for 30 minutes, then whiz in a blender to fine crumbs.) Spread a quarter of the frosting over each layer and stack them up (using less than a quarter if you’re making four layers). Smooth the top and frost the sides of the cake.
8. To decorate with cake crumb, place a stencil or a shape cut out of parchment over the cake top and sieve the crumbs all over the cake. Using a pastry brush cover the bald patches and brush the crumbs off the stencil, then lift it.