How to cook
Beat the eggs with the sugar and vanilla to a creamy consistency. Add the oil, baking powder and yoghurt, then begin adding the sifted flour, while alternating between it and the warm water. Stir with a wooden spatula until the mixture absorbs the flour and water and you get a homogeneous, thick, cake dough.
Grease a cake form with removable sides and pour the mixture into it. Put jam on top in several spots and sprinkle on pieces of crumbled chocolate.
Don't stir or touch the chocolate, just drop the pieces carefully into the mixture, without pressing on them because otherwise they're going to sink to the bottom.
It's best if the chocolate pieces are large. If the mixture is thick enough, they will remain on top. Use quality dark chocolate; milk chocolate would simply melt and you won't get the same effect.
Bake the cake in a preheated 338°F (170 °C) oven for 40-50 min. until your toothpick comes out dry when you poke it.
Finally, take it out of the form, leave it to cool for 10 min. and sprinkle with powdered sugar if desired.