"In the black" italian chocolate mousse - yum!

I extracted this recipe from a book written by Marcella Hazan. Marcella was born in Censenatico on the Adriatic coast of Italy. With a doctorate in natural sciences and biology under her belt she settled in the big apple New York after marrying an Italian American.There she began giving Italian cooking classes and like Julia Childs, she started giving Italian cooking lessons in her apartment and eventually became a chef with a household name purely by love of and life dedication to cooking food.
Here is her foolproof chocolate mousse recipe (not budget).

Ingredients

170g finely chopped semi sweet chocolate
4 eggs
2 tsp caster sugar
4 tbsp strong espresso
3 tbsp dark rum
mixing bowl kept in freezer
150 ml cold whipping cream

Method

To melt chocolate the modern way, take a bowl, fill it up with boiling water, stack another on top with chocolate in it.
Separate eggs, put the yolks in a separate bowl together with the sugar and beat them until they become pale yellow and creamy. Add the melted chocolate, coffee, rum and mix them in with a spatula until the ingredients are uniformly combined.
Take the bowl out of the freezer, put in the cream, beat it with a whisk until it stiffens, then fold it into the chocolate and egg yolk mixture.
Put the egg whites into a bowl, whip them until they form stiff peaks, then fold them gently but thoroughly into the chocolate mixture.
Pour the mousse into 6 individual serving cups or goblets, cover with cling film and refrigerate overnight.

it can be kept for 3 or 4 days, but after the 24 hours it may wrinkle and lose some of its creamy consistency.