200g/7oz dark chocolate, broken into pieces
5 medium (US large) eggs, separated
175g/6oz/¾ cup caster (superfine) sugar plus extra to sprinkle
1l/1¾ pints/4 cups soft-scoop vanilla ice-cream
hot chocolate sauce to serve
1 Preheat the oven to 180°C/350°F/Gas 4. Line a 35 x 23cm/14 x 9in deep roasting pan with parchment paper.
2 Melt the chocolate in a bowl set over a pan of simmering water. Whisk the egg whites in a large bowl until stiff. Whisk in one-third of the sugar, a little at a time, until thick. In a separate bowl, whisk the yolks with the remaining sugar until pale and thick. Fold in the melted chocolate, then fold in the egg whites gently but thoroughly.
3 Pour the mixture into the prepared tin and bake in the oven for 15 minutes or until just set. Set aside for several hours.
4 Sprinkle a sheet of parchment paper with sugar. Turn the chocolate sponge out on to the paper and peel away the backing parchment. Spoon the ice-cream evenly over it and roll up the sponge in the paper, starting with the short edge.
5 Overwrap the paper with foil, twist the ends to seal, then freeze for 4 hours, or overnight.
6 Serve the frozen roulade cut into slices with the hot chocolate sauce.