1. Beat the egg yolks and lemon juice with 30ml water. Reserve
15ml of the castor sugar, then add the remaining sugar to the
egg yolks and beat until thick and creamy.
2. Sift the flour, baking powder, cocoa and a pinch of salt, and
fold into the egg yolks. Beat the egg whites with the reserved
castor sugar until stiff. Fold into the cake batter. Pour into
a greased and lined Swiss roll tin and bake in a preheated
oven for 10 to 12 minutes.
3. Sprinkle a little castor sugar onto a slightly damp dishcloth.
Remove the cake from the oven and turn out onto the cloth.
Remove the baking paper and slice off the edges of the cake.
Sprinkle with half the liqueur, roll up and set aside to cool.
4. Stir the remaining liqueur and the castor sugar into the
mascarpone. Unroll the cake and spread with the filling,
then roll up again. Refrigerate until ready to serve.