Lightly butter a baking tray 22cm x32cm then line with baking parchment
For the sponge, place the eggs and half the sugar in the bowl of a food mixer with the vanilla. Put the remaining sugar onto a tray and heat through in the oven for a few minutes.
Whisk the eggs and sugar on high speed until pale and thick. Remove the sugar from the oven and whisk this in until well combined.
Sift in the flour, then carefully fold in to combine.
Spoon onto the prepared tray spread to cover so it is even
Pop in the oven and bake for 12 minutes.
While the sponge is cooking, place a damp, clean tea towel on a large tray or board.
Cover with a sheet of baking parchment.
When the sponge is ready, sprinkle the baking parchment liberally with caster sugar and then carefully tip the sponge on top of the paper. Remove the paper off the underside of the sponge. Leave to cool.
Once cool, whip the cream, sugar and vanilla together. Spread the jam over the sponge then the cream.
Scatter over the berries, then roll up the sponge to enclose the filling ingredients, using the towel and paper to help tighten the roll.
Unroll the towel and paper from the sponge roll. Dredge with more caster sugar if liked and serve in slices.