Heat oven to 350. Grease two 8-inch cake tins and line with parchment paper. Weigh the eggs first (in their shells), then weigh the same quantity of sugar and flour. For the butter and the margarine, you need half the weight of the eggs.

In a large bowl, cream the butter, margarine and sugar together using an electric whisk until pale in color and light and fluffy. Scrape down the sides of the bowl and beat again.

Beat the eggs together, then gradually add to the mixture, beating well after each addition. Scrape down the sides of the bowl and mix again.

Sift the flour over the surface of the mixture and gently fold in, using a large metal spoon.

Divide the mixture between the prepared tins. To ensure the cakes are exactly the same size you can weigh the cake mixture into each tin. Gently smooth the surface with the back of the spoon to level it.

Bake in the center of the oven for 25 minutes until risen, golden brown and the cakes spring back in the centre when lightly touched with a fingertip. They should be slightly shrunken away from the edges of the tin. Leave the cakes in the tins for 5 minutes, then remove to a wire rack. Leave to cool completely.

In a medium mixing bowl, beat the cream, confectioners’ sugar, and ½ teaspoon of vanilla on medium speed just until stiff peaks form.

When cool, sandwich the cakes together with the whipped cream and jam, and sprinkle the top with a little caster sugar.