How to cook
Crumble the chocolate into pieces and melt it in a water bath with the butter and milk. Once removed from the water bath, add the yolks one by one and then add the sugar.
Beat the egg whites into a thick, snowy substance, with 1 pinch of salt. Add the whites to the chocolate and then stir vigorously.
Add the rest and stir until there's no visible trace of the egg whites left. Serve the Chocolate Mousse cold with some grated chocolate.