For the white chocolate mousse with tonka bean, beat the egg and the egg yolks in a water bath until creamy. Soak the gelatine in cold water.
As soon as the mixture starts to become creamy, remove the bowl from the water bath and add the gelatine. Finely grate the tonka bean and gently mix it in.
Stir with a whisk until everything has cooled down. Melt the white cooking chocolate in a water bath and gently fold into the egg mixture. Add rum and creme de cacao to taste.
Fold in the whipped cream and chill in the refrigerator with the lid closed for at least 2 hours.
Arrange the white chocolate mousse with tonka bean and serve.