Chocolate mousse

For another biologists' dinner, I brought dessert. As there were lots of kids, I made chocolate mousse, a suggestion of D. I don't eat chocolate myself so I also made an apple tart.
I found a recipe in the series 'La cuisine de A à Z' from 1970, belonging to my mother and before that to my grandparents I guess. When I started cooking as a kid, I often looked to these books.

Serves 4-5

200 g cooking chocolate
30 g butter
4 eggs
50 g sugar
1 packet vanilla sugar

Heat chocolate and butter at very low heat until the mixture is molten.
Add egg yolks to sugar and vanilla sugar and whisk until creamy.
Take chocolate off heat and add egg yolk mixture. Stir well.
Beat egg whites until very stiff, then add them gently to the chocolate.
Keep in the fridge for a few hours.

Note: if there are no children you might add a bit of cognac

A photograph might follow, if I remember to take one of the few spoons that are left.