Butter a swiss roll tin and line with buttered grease proof paper.
Place the eggs and sugar into a bowl over a pan of hot water and whisk until the mixture is pale and leaves a thick trail. Remove from the heat.
Sift half the flour and salt over the egg mixture and fold it in carefully using a large metal spoon. Repeat with the remaining flour, then add the hot water.
Turn the mixture quickly into the prepared tin, tilting carefully until the tin is covered evenly. Bake at once just above the centre of the oven, at 425 degrees F (200 degrees C) gas mark 7 for about 9 or 10 minutes.
Gently warm the jam thoroughly over a low heat.
When cooked remove the cake from the oven and quickly place it on a sugared surface or cooking paper.
Spread the jam or other filling evenly over the cake when cool.
Carefully roll the cake from the short side using a tea towel or baking paper.
