Mix the sugar with the butter. Add the egg yolks one by one, then the yoghurt, and flour sifted with the baking powder. Pour the mixture into a buttered baking dish and bake in a moderate oven at 356°F (180 °C). Meanwhile, beat the egg whites with the powdered sugar into thick snow.
Cover the still warm baked cake with jam, sprinkle it with chopped nuts and top with the beaten whites. Use a spoon to make ripples, sprinkle it with nuts and bake until pale pink in a low oven, as you would for meringues.
Sprinkle the top with chocolate. Cut the cooled cake into slices. Enjoy!