To make chocolate truffles you will need:
The evening before, break the chocolate up into pieces and ask an adult to melt it, together with a spoonful of water, using a bowl over a saucepan of water.
Take it off the heat, add the butter (cut into thinnish slices) and let it melt, then mix with a whisk until you have a smooth paste.
Add the heavy cream and the egg yolks (be very careful not to add in any egg white).
Mix until you have a smooth, creamy mixture.
To help the paste harden, place the bowl containing the mixture into a refrigerator for at least 3 hours.
Bring the bowl out, then scoop out a little paste with a spoon.
Roll the paste into little balls with your hands.
Then roll the balls in the cocoa powder.
Keep them in the refrigerator.