Tiramisu

Melt chocolate and use to make 6 gondola shapes on baking parchment.
Chill until set and carefully peel off paper. (This step is optional).
Coat inside of 6 paper cupcake cases with melted chocolate. Chill until set, then coat again.
Repeat until all chocolate has been used. (If you did not make gondola shapes, use just enough chocolate to coat to desired thickness.) Carefully peel away paper.

Beat egg yolks and icing sugar until pale yellow and almost doubled in volume. Beat in mascarpone (do not overbeat).

Whisk egg whites until stiff, with remaining sugar. Fold in cheese mixture.
Halve sponge fingers crossways. Dip biscuits in coffee and place 2 halves in each chocolate case.
Spread a little cheese mixture on top.
Repeat biscuit layer. Pipe remaining cheese mixture on top. Chill.
Dust with cocoa powder, top with a gondola and serve.