Wash the lemon well, dry it and rub the peel thinly, then cut in half and squeeze out.
Slit open the vanilla pod and scrape out the pulp
Boil the buttermilk with sugar, grated lemon peel, juice and the vanilla pulp .... I also boiled the vanilla pod with it .... let it steep for 30 minutes away from the stove
soak the gelatine in cold water
Remove the vanilla pod from the buttermilk and stir in the squeezed gelatine until it has dissolved
then beat in a cold water bath ... then put in the refrigerator until the mixture starts to gel
In the meantime, whip the cream until stiff and fold into the buttermilk mixture
Fill the mousse into glasses or bowls and let it set in the refrigerator, preferably overnight