With the point of a large needle or knitting needle, make a small hole on the head of the egg. Be careful to not press too hard (don't broke the egg).
Repeat with all the eggs. NOTICE : for the chocolate cake, set aside the content of 4 eggs in an other bowl.
With the rest of eggs : omelet party !!
Once empty, wash the eggs shell with hot water. Fill them, shake delicately and drain. Repeat it two more times. Set aside.
Let's make the chocolate cake :
Preheat your oven at 180°C/350°F.
Melt the butter and the chocolate in microwaves or in a double boiler. Mix together.
In a bowl, mix the 4 eggs wtih sugar.
Add the flour and mix well.
Pull a little bit of melted butter in each shell, shake well, pour out the excess and let drain on paper towel.
Fill each shell to 3/4 with a piping bag (only at 3/4 to not burst the shell during cooking time).
Put the eggs in the muffin tin.
Let cool down when the chocolate cakes is baked inside.
If you want, you can decorate the eggs shell when they are cooled. Painting, glitters... About me, I choosed some Kawaii spirit. With a thin pencil, draw delicately your picture (if it's not good, just erase it). Then with a thin black felt, brush on the pencil marks. That could be a great creative workshop with children ^^