Preheat the oven to 200°C and line a Swiss roll tin with baking paper.
Beat the eggs and sugar together until light and frothy, then sift the flour into the mixture. Carefully mix until smooth.
Pour the batter into the tin, then bake for about 10 minutes, until it’s light brown and coming away from the tin at the edges.
Place a large sheet of baking paper on a work surface and sprinkle with icing sugar over it.
Turn out the sponge onto the sugary sheet then and peel off the baking paper. Leave it to cool.
Cut the edges off (about 5mm) then cut the sponge into 3 equal rectangular shapes. Spread jam on top of 2 then put them on top of each other (the one without jam should go on the top – with the sugary side facing upwards.)
Cut the jam sponge sandwich into little squares, then dust with some more icing sugar. Serve on the same day of baking.