1. Preheat oven to 200°C/400°F/Gas 6. Grease and base line a 23cm/9" tin or two 18cm/7½" sandwich tins with greaseproof paper.
2. Place the three egg whites and pinch of salt in a large, clean, dry mixing bowl. Stiffly beat until mixture is dry looking in appearance.
3. Next, add the sugar and beat for a few seconds. Then add the egg yolks and beat until mixture thickens and the trail of the beaters is visible.
4. Finally, sieve in the flour and fold it into the thick mixture using a metal spoon. To fold, cut through the mixture over and over with the metal spoon until all the flour is blended. (Never beat as it will beat out all the air!)
5. Fold in the vanilla essence, if used. Then transfer to the prepared tins and bake for about 15 minutes.
6. As soon as sponge is baked, transfer to a wire tray to cool.
7. When cold, sandwich with jam and whipped cream.