Dough for the layers:
150 g sugar (5 1/2 oz)
300 g butter (10 1/2 oz)
1 tsp baking powder
400 g all purpose flour (14 oz; plus some additional flour for dusting the workspace)
Mix together the butter and sugar until fluffy, then add the egg, baking powder, and flour.
Make the dough into a big ball, then divide it in 4.
Put it in the refrigerator, covered with a paper towel, for 30 minutes or until it is cooled. Take 1 ball out and stretch it on a floured working top with a rolling pin and make a rectangle of 9 x12 inches. The dough should be cold but not hard before stretching it. Try not to use a lot of flour, since that will change the consistency and the taste.
Roll it up on the rolling pin and transfer it onto the baking tray.
Bake it at 350° F (180° C) for 10-12 minutes. It is ready when it is slightly brown at the edges, as in the picture below. Carefully remove it from the tray while it is still warm, and place it on a rack to cool. You may need to gently slide a knife or spatula between the cake layer and the pan to get it to slide off easily.
Repeat the steps above with the rest of the dough. When the baked sheets are cold, spread apricot jam on one, then place another cake layer on top and repeat, except on the top layer, which will be covered with icing.
150 g (5 1/2 oz) chopped walnuts
4 egg yolks
150 g (5 1/2 oz) powdered sugar
In a pan mix together 4 egg yolks with 150 g (5 1/2 oz) powdered sugar (preferably granulated sugar ground at home into powdered sugar, not sugar bought in powdered form from the store, as it should not have cornstarch in its composition). Place this pan on top of/into another pan with boiling water, and keep stirring until the composition is hot and looks creamy (see picture below.) Then add a few drops of vanilla essence and stir.
When it is done, pour the icing onto the top layer of the cake and immediately scatter the walnuts on it, pressing them down with your palm.
After a few hours, you can cut it into small bars.
Note: Making the layers can be really hard and frustrating the first time you try, but don't be discouraged! With practice, this is going to become a favorite recipe that everyone will ask you to make over and over again.