Soak the gelatin. Mix the cream cheese with the buttermilk, sugar and vanilla sugar. Heat the lemon juice and dissolve the gelatin in it. Whip the cream until stiff and fold into the mixture. Leave to set in the refrigerator overnight.
The next day, puree the strawberries and sweeten to taste with the powdered sugar (I take about 1/2 packet). Just before serving, pour the strawberry puree over the cream.