Mix the ingredients except the chocolate to a smooth batter. Depending on the size of the eggs, you may need a little more mineral water.
Use a hammer to grind the still wrapped block chocolate into large pieces and add to the dough. Make sure that the pieces are relatively large so that the block chocolate is not completely melted after baking and the chocolate pieces remain in the cake.
Put the dough in a 26 cm form and bake at 180 ° C for about 60 minutes.
Due to the reduced amount of flour compared to a normal sponge cake, the cake is nice and juicy and not too dry. Those who like sticky brownies will love this cake.