Place one gelatin sheet in a bowl of cold water.
Melt the chocolate au bain-marie. Make sure the water does not boil and do not stir the chocolate.
Whip up the cream and put the whipped cream in the refrigerator.
Then separate both eggs and beat the egg yolks with 25 grams of granulated sugar until fluffy. Cut a vanilla pod in half, scrape out the marrow and mix it into the egg yolk mixture.
Remove the pan with chocolate from the other pan (with water) when the chocolate has melted. Test this by lightly piercing the chocolate with a fork. Then take your gelatin sheet from the cold water and dissolve it in 1 tablespoon of hot water. Mix this hot gelatine water into the melted chocolate with a whisk until it's a nice smooth mass.
Mix the egg yolk mixture and the chocolate in a bowl and let it cool briefly.
In the meantime, beat the egg whites until stiff with a hand mixer or kitchen machine (make sure you only have egg whites (not part of the yolk) and that you use a bowl that is really clean and free of grease). When the egg whites are stiff and fluffy, add a bag of vanilla sugar and beat again until the sugar is well mixed into the egg whites.
Then mix the whipped cream and the stiff egg whites into the chocolate mixture with a whisk (make sure the chocolate mixture is not still warm, otherwise the mousse will curdle).
Divide the mousse among 4 glasses and place them in the refrigerator. Let them set for at least 2 hours (but make sure it's actually set before you poor over the orange juice).