Beat the eggs until frothy with the sugar and vinegar in a large bowl.
Mix the baking powder into the flour and alternately add portions of flour and milk to the frothy eggs.
Whip the two egg whites stiff with a pinch of salt and gently fold them into the mixture.
Heat a large frying pan and grease it with some butter. Place 3 tablespoons of batter a little apart in the warm pan, place a piece of chocolate on top, cover with a spoonful of batter, and let it cook for about 2 minutes over medium heat. Flip them over and let the other side cook for another minute. Cook the entire batter this way.
Tips
Just the best with some powdered sugar on it.