ready in 37 min.
Heat the oven to 200°C (180°C in a fan oven), 400°F, gas 6 and line a baking tray with grease-proof paper.
Whisk the egg whites with the lemon juice until stiff. Slowly trickle in the sugar and continue beating until stiff. Mix together the flour and cornflour. Tip the egg yolks on top of the whisked egg whites and sieve over the flour mixture. Fold in. Pour the light sponge mixture onto the baking tray, smooth flat and bake in the centre of the oven for 10-12 minutes.
Sprinkle sugar over a large tea towel and carefully turn the cake out onto the tea towel. Brush the grease-proof paper with cold water and carefully peel away from the cake. Roll up the cake immediately using the tea towel and leave to cool.
Once cooled, unroll the cake and spread with jam. Roll up again, then cut into slices and serve.