Step 1: whisk together the egg and the egg yolk in a heatproof bowl and set aside.
Step 2: without turning on put the chocolate and butter in a blender.
Step 3: take a medium pot and add the rest ingredients. Here you will begin with milk, cream, sugar, cocoa, cornstarch and a pinch of salt.Stir appropriately until you see a smoother mixture. Allow it to boil while you are gently whisking. Give it time for about two minutes to bubble.Immediately it thickens, turns the heat off the pot immediately. Over boiling the cornstarch will lead to thinning and this can spoil the recipe.
Step 4: add a little cornstarch mixture into the eggs. Stir instantly as you add to avoid cuddling.
After that, add the remaining eggs together with the rest cornstarch mixture. Cook over low heat as you whisk constantly until it simmers. Pour into the food blender immediately before it cools. Run the machine until you obtain a smooth pudding.
Step 5: the chocolate mousse is now ready for consumption except for few garnishing. Pour into individual bowls and wrap with a clinging film. Chill in the fridge for 2-3 hours, or until set.
Decorate with chocolate shavings and enjoy with the whipped cream fraiche.