Preheat the oven to 180C/350F/Gas Mark 4.
Grease and line an oblong (13 x 9 inch) tin with parchment paper.
In a mixing bowl beat the 4 eggs with the sugar for the sponge base. It should become very light and aerated. The whisk should leave a figure of eight pronounced on the surface of the mixture when the whisk is lifted out of it.
Gently fold in the sifted flour with a metal spoon. Be very gentle so as not to knock any of the generated air out of the sponge base but also ensure that all of the flour is incorporated. Pour the mixture into a prepared Swiss roll tin.
Bake for 20 minutes, until well risen and golden brown and take the sponge out of the oven.
Before the sponge is fully cooled, invert it onto a sheet of parchment paper dusted with the caster sugar (50g) and spread with a thin layer of raspberry jam.
Carefully roll the Swiss roll up from the longest side rather than from the shortest.
Roll and slice into portions.