Stir everything again until the sugar melts. Finally, add 1 cup sifted flour (with 1 vanilla added beforehand) to the mixture. Stir again.
Pour it into a form - I used a standard baking cake form with a ring, to make it easier to remove the bottom afterward. Bake in a preheated 356°F (180 °C) oven for about 20-30 min.
Once it rises and becomes golden-colored, check with a toothpick to see if it's ready and remove from the form. While still hot, smear it generously with homemade prune jam - it soaks into the cake layer very well.
Leave the smeared cake layer aside and get to work on the egg whites.
You need a glass or plastic bowl to beat the egg whites in, plus it needs to be absolutely dry and clean. Gradually beat from a low to a higher speed and slowly add 10 tbsp sugar (can use less but I prefer it sweet).
Once the whites become stiff, distribute them onto the cake. To make it even prettier you can make tips with the back side of the spoon - put it by the whites and pull the spoon upward abruptly. It becomes very beautiful.
Return the cake to the oven at lower heat (302°F (150 °C) max) and bake until the whites take on a golden hue - about 15 min.