Squeeze the lemons and heat the juice. Dissolve the gelatine in the warm (not boiling) lemon juice. Mix with buttermilk and powdered sugar. Whip the cream until stiff and fold in carefully. Chill for 8-10 hours.
Cut off the cams with 2 tablespoons and serve, for example, on a mirror made of fruit sauce (made from pureed fruits) and / or with fresh mint.