Into a saucepan under low heat, add some water and wait until it makes some steam. Then inside a bowl sitting on top of the pan, add in the Semi-Sweet Dark Chocolate (300 gram), Butter (125 gram) and stir gently until the mixture melts.
Once the mixture is melted, add in the yolks from the Egg (4) and whisk them through until completely combined. Take the bowl off the heat and set aside.
In a separate mixing bowl, add and whisk the egg whites from the eggs you have used before. To that add in and mix the Caster Sugar (2 tablespoon)
Then, gently fold the egg-white mixture into the chocolate mixture.
Then, pour the mixture into cups and put them into the fridge for about 4 hours before serving.