Soak gelatine in cold water. Wash lemons hot, dab dry. Rub the peel off one fruit. Cut three slices from the second lemon for decoration. Squeeze both lemons.
Separate eggs. Beat the egg yolks and sugar until frothy. Stir in yoghurt, lemon juice and zest. Squeeze the gelatine, dissolve and stir into the lemon-egg cream. Chill. As soon as the cream starts to gel, beat the egg whites until stiff and fold in.
Pour cream into dessert bowls and chill for about 2 hours. Quarter lemon slices and decorate the lemon cream with them. Decorate as you like with some lemon balm and julienne.