Enjoy a light and airy sponge, coated in crunchy sugar and bursting with fruity jam for a vintage teatime treat.
1. Heat the oven to 200C/fan 180C/gas 6. Butter and line the base and sides of a 23cm x 34cm x 2cm swiss roll tin. Whisk the eggs and caster sugar for 3 minutes with an electric hand whisk until thick and pale. Add the vanilla and whisk for another few seconds. Sieve in the flour and baking powder in two batches, then use a large metal spoon to fold the flour into the batter. As you fold, gently lift and shake any large pockets of flour to break them up.
2. Once the batter is just combined, carefully pour into the tin, using a spatula to scrape the bowl clean. Ease the batter to the corners of the tin and lightly smooth the top. Bake for 10-12 minutes until golden and springy.
3. While the sponge is baking, cut a large rectangle of baking paper. Dust the paper with the extra caster sugar. Once the cake is cooked, tip the sponge onto the sugared paper and peel off the lining paper. Push the short end of the sponge 2cm away from the edge of the paper. Fold the edge of the paper onto the short edge of the sponge and roll both up together while the sponge is still warm. Leave to cool rolled up.
4. Stir the jam to loosen. Carefully unroll the sponge, but don’t flatten it completely or it will crack. Use a palette knife to cover the inside of the sponge with the jam and then roll it up again without the paper. Put on a plate seam-side down to serve.