Marbled swiss Roll

Directions

1. 1. Preheat over to 2000C / 4000F / Gas 6. Grease 30 x 20 cm /12 x8 in Swiss roll tin and line with non-stick baking paper. Sift half the flour with the cocoa into a bowl . Stir in the grated plain chocolate. Sift the remaining flour into another bowl. Stir in the grated white chocolate.
2. 2. Whisk the eggs and sugar in a heatproof bowl set over a saucepan of hot water until it holds its shape when the whisk is lifted and a ribbon trail remains.
3. 3. Remove the bowl from the heat and tip half the plain chocolate mixture into one portion, then fold the white chocolate mixture into the other. Stir 15ml / 1 tbsp boiling into each half to soften.
4. 4. Place alternate spoonfuls of mixture in the prepared tin and swirl lightly together with a knife or slim metal skewer for a marbled effect. Bake for about 12-15 minutes or until the cake is firm and the surface springs bake when touched with a fingertip. turn the cake out on to a sheet of non-stick baking paper placed flat on the work surface.
5. 5. Trim the edges to neaten and cover with a damp, clean dish towel coo.
6. 6. For the filling, mix the chocolate butter-cream and walnuts in a bowl. Uncover the sponge, lift the lining paper and spread the surface with the buttercream. Roll up carefully from a long side and place on a serving plate. Slice to serve and store in an airtight container.