This light, almost fat-free sponge, rolled up around a raspberry and passionfruit filling, makes a very pretty dessert. It's ideal for late summer, when raspberries are particularly sweet. Serve with homemade custard, if desired.
Filling: Place half the raspberries and the icing sugar in a bowl and crush lightly with a fork. Stir in the passionfruit pulp.
Sponge: Preheat the oven to 200 degrees C. Grease a 23×33cm Swiss roll tin and line the bottom with baking paper.
Place the eggs and sugar in a large bowl and beat with an electric mixer until the mixture is very thick, pale and leaves a trail on the surface when the beaters are lifted out.
Sift half the flour over the mixture and gently fold in with a large metal spoon. Sift over the remaining flour and fold in together with the tepid water.
Pour the mixture into the prepared cake tin and shake gently to spread it evenly into the corners. Bake for 10–12 minutes or until the sponge is well risen, pale golden and springs back when pressed lightly.
Turn out onto a sheet of baking paper that is slightly larger than the sponge. Peel off the lining paper. Remove the crusty edges of the sponge with a sharp knife and make a score mark 2 cm from one of the shorter edges all the way along. (This will make the sponge easier to roll up.)
Spread the fruit filling over the hot sponge, leaving a 1 cm border all round. Scatter over the remaining half of the raspberries. Carefully roll up the sponge, starting from the edge with the score mark. Place the roll, seam-side down, on a plate.
To Serve: Serve warm or cold, cut into slices. Decorate each serving with a few extra raspberries and a sprig of mint.