Grease a 26cm x 32cm Swiss roll pan. Line with baking paper,
extending 2cm above pan edges.
Place eggs, sugar and essence in bowl of electric mixer. Beat for 8
minutes, or until thick. Fold
in combined sifted cornflour, cream of tartar and soda. Pour into pan. Tilt to move into corners.
Cook in
moderate oven (180°C) for 12 minutes, or until sponge
springs back when touched. Turn onto a baking paper-lined tea towel dusted with extra caster sugar. Peel
away top layer of paper. Roll up sponge from one short side. Cover with a tea
towel. Cool.
Place
chocolate in a heatproof bowl over simmering water and
stir until almost melted. Remove and stir until melted. Cool slightly.
Beat cream with mixer until soft peaks form. Beat in chocolate.
Unroll sponge. Spread with filling, leaving 2cm border. Re-roll. Move
to serving plate, removing the baking paper. Decorate with raspberries and
curls.