Despite appearances, Swiss rolls are in fact very simple to make. The cake itself has no butter in it, so you can feel justified in spreading it with lashings of jam and whipped cream. Use any kind of jam you like; apricot or blackberry, for instance, would do just as well as raspberry or strawberry.
Preheat the oven to 375 degrees F.
Line the base of a 10 by 15-inches Swiss roll or jelly roll pan with greaseproof or parchment paper. Brush the base and sides of the pan with melted butter, and dust with flour.
In a large bowl or in an electric food mixer, whisk the eggs, and sugar together, until light and fluffy, and then add the water, and vanilla extract.
Sift in the flour, about a third at a time, and using a large metal spoon, fold it into the egg mixture.
Pour the mixture gently into the prepared pan, and bake in the oven until the center of the cake is slightly springy and the edges have shrunk a little from the sides of the tin, about 12 to 15 minutes.
Spread out a piece of parchment paper (slightly larger than the tin in size) on a work surface and sprinkle evenly with caster sugar (this stops the roll from sticking to the paper). Turn or invert the pan onto the sugared parchment paper, and then carefully remove the tin and parchment paper from the bottom of the cake.
Place a slightly damp, clean tea or kitchen towel over the cake while it cools- this will prevent it from drying out and cracking when you roll it.
When the cake is cool, spread the jam sparingly over the cake, leaving a 1-inch border. Repeat with the whipped cream. With the longest side facing you, roll up the Swiss roll away from you, then transfer to a plate to serve. Sprinkle the cake with caster sugar or dust with icing sugar to finish.