50g plain chocolate, 70&37; cocoa solids or more, very finely chopped
250g mascarpone light
50g icing sugar
1 ½ tbsp cocoa powder
1 tsp instant coffee granules
½ tsp vanilla extract
Heat oven to 190C/170C fan/gas 5. Lightly oil and line a 23 x 32cm Swiss roll tin with baking paper. Mix the coffee with 1 tbsp warm water. Beat the eggs, both sugars and the coffee mix together in a large mixing bowl with an electric whisk for about 8 mins or until the mixture is thick and airy like meringue and holds a trail when you lift up the beaters.
Sift the flour and cocoa powder over the fluffy egg mix, then fold in very gently using a large metal spoon. Pour the mixture evenly into the lined tin and carefully tip it so it spreads evenly without being deflated. Use a knife if necessary to very gently tease it into the corners. Bake for 12-15 mins or until the cake feels spongy but firm when touched.
Lay a sheet of baking paper on the work surface and sprinkle with a little caster sugar. Tip the tin upside-down onto the paper and let the cake fall out. Carefully peel off the paper. Roll up the cake lengthways from one of the short ends with the help of the paper, rolling it inside so the cake doesn’t stick. Cool. The cake becomes even more moist if left overnight wrapped up, then iced the next day.
For the chocolate icing, put the chopped chocolate in a medium bowl. Heat a small pan of water (one-third full) until boiling, remove it from the heat, then sit the bowl of chocolate over the top. Leave for a few mins off the heat until melted. Remove the bowl from the pan, then leave the chocolate until it is cool to the touch. Beat the mascarpone and quark together, then sift and stir in the icing sugar and cocoa powder. Stir in the cooled melted chocolate (keeping a couple of tsp back for drizzling), then the coffee mixed with the vanilla extract.
Carefully unroll the cake, don’t worry if it cracks a bit, and discard the paper. Spread half the icing over the unrolled cake, then re-roll it, finishing with the join underneath. Place the cake on a serving plate. Swirl the rest of the icing all over the cake to cover it, then drizzle over the reserved melted chocolate. Decorate with a sprig of holly.