Beat the eggs, sugar and vanilla sugar with a mixer into fluffy cream. Add the yoghurt and oil and stir with a spatula.
Add the pre-mixed and sifted together flour and baking powder and stir slowly from the bottom going up until you obtain a homogeneous mixture.
Next add the prune jam and stir in the same way briefly. Pour the mixture into an oiled and slightly floured cake form, place in a preheated 356°F (180 °C) oven, bake until ready about 35 min.
Once cooled a bit, take the cake out of the form and into a suitable plate.
Prepare the glaze by melting the chocolate in the cream into a smooth mixture. While still hot, smear a layer of it onto the cake with a brush, then once cooled and slightly hardened, pour on the rest of the glaze. For a more stunning effect, use a chocolate with nuts.