Preheat the oven to 180°C/Fan 160°C/Gas 4. Lightly grease two deep 20cm loose-bottomed sandwich tins and line the base of each with non-stick baking paper.
Measure all the cake ingredients into a large bowl and beat for about 2 minutes with an electric mixer until beautifully smooth and lighter in colour. The time will vary depending on the efficiency of the mixer. Divide the mixture evenly between the tins and level the surfaces.
Bake in the preheated oven for about 25 minutes, or until well risen, golden and the cakes are shrinking away from the sides of the tin. Leave to cool in the tins for a few minutes then turn out, peel off the baking paper and finish cooling on a wire rack.
When completely cold, sandwich the cakes together with the jam and whipped cream. Sprinkle with caster sugar to serve.