Heat the oven to Gas 3, 325F, 170C. Butter two 18cm (7 inch) cake tins and line with greaseproof paper. Cream the butter and the sugar together until pale and fluffy. Whisk the eggs in a jug and add slowly to the mixture beating well. Add a few drops of vanilla essence then add sieved flour slowly to the mixture, folding in carefully to preserve the air. If the mixture is very stiff add some milk. Divide between the two tins and cook in the middle of the oven for about 25 - 30 mins. They are ready when the centre feels springy when touched with your finger. Cool for 5 mins and then turn out onto a cake rack. Peel off the paper. Spread the bottom cake with jam and top with whipped cream. Sandwich the other cake on top. Dust with sugar and enjoy!