Serves eight to 10.
YOU WILL NEED
For the sponge 130g/4½ oz plain flour
2 tbsps cocoa powder
½ tsp bicarbonate of soda
Pinch of salt
120ml/4fl oz buttermilk
1 tsp vanilla extract
1 tsp white-wine vinegar
120g/4oz unsalted butter, softened
150g/5½oz caster sugar
1 large egg
1½ tbsps red gel paste colouring
30ml/1fl oz water For the filling 250g/9oz full-fat cream cheese, such as Philadelphia
130g/4½oz white chocolate, melted
50g/1½oz unsalted butter, well softened
50g/1½oz icing sugar, sifted, plus extra for dusting Equipment One 32 x 23 x 2cm/13 x 9 x ½in Swiss roll tin
Pre-heat the oven to 180°C/350°F/ Gas Mark 4, and line the Swiss roll tin with baking parchment.
Sift together the flour, cocoa powder, bicarbonate of soda and salt. In a jug, mix together the buttermilk, vanilla extract and white-wine vinegar.
In a freestanding electric mixer with a paddle attachment, or using a hand-held electric whisk, cream the butter and sugar together until light and fluffy. Add the egg and mix well. Scrape down the sides of the bowl.
With the mixer or whisk on a slow speed, add the dry ingredients gradually to the creamed butter and sugar, alternating with the buttermilk mixture. End with an addition of dry ingredients.
Dissolve the red gel paste colouring in the water, making sure the paste is completely dissolved and there are no lumps of paste left in the water.
Add the dissolved paste mixture to the batter, making sure the colouring is evenly mixed throughout.
Spoon the batter into the prepared tin and spread to the edges. Bake for approximately 25 minutes, or until the sponge is set on the top and springs back when lightly touched. Remove the sponge from the oven and cover with a damp tea towel. Allow the sponge to cool a little.
While the sponge is cooling, make the filling. In the electric mixer with the paddle attachment, or using the hand-held electric whisk, beat the cream cheese until it is smooth.
With the mixer or whisk on a medium speed, pour in the melted white chocolate, mixing until it is incorporated in the cream cheese. Then add the butter, mixing well.
Now, add the icing sugar and beat until the filling is smooth and fluffy.
Dust a sheet of baking parchment or a clean tea towel with icing sugar. Loosen the edges of the cake and invert the sponge on to the parchment or tea towel.
Beginning at the narrow edge of the sponge, roll the sponge and the parchment or towel up together. Cool completely on a rack, seam-side down, for 10-15 minutes.
Once cooled, gently unroll the sponge and carefully peel the paper from the top of the sponge. Spread the filling over the inside of the sponge roll. Re-roll the sponge without the parchment or tea towel.
Dust with icing sugar and serve.