Weigh the eggs. Then, measure out the same amount, in weight, of the flour, sugar and butter.

Cream the butter and sugar. Then add the salt and sift in the flour. Mix together thoroughly.

In another bowl, whisk the eggs thoroughly until frothy. You could choose to add a few drops of lemon juice to help with this.

Add the beaten eggs to the mixture with the dry ingredients. Beat the whole mixture for no less than 10 minutes by hand, or 3 minutes by electric mixer. Since there is no raising agent, this must be done for a sufficiently long time.

Pour the mixture into a buttered and floured 9x9 pan. Bake at 160°C fan-forced or 180°C conventional for 25-35 minutes on the middle rack, rotating the pan around half way.

Remove from oven once the top is a light-golden brown, springs back when pressed and a tester comes out clean. Let cool for a few minutes.

Remove cake from the pan and cut into long finger pieces. Halve these pieces horizontally and spread the jam or marmalade in the middle, then press them back together. Pile in cross bars on a dish. Serve.