Mix the gelatine with a little lemon juice and let it swell according to the instructions. Mix the remaining lemon juice with the sugar, amount to taste, and whisk in the yogurt. Stir the gelatine into the lemon yogurt. As soon as the mass thickens creamy, whip the cream until stiff and mix in.
Pour the cream into dessert glasses and leave to set in the refrigerator until ready to serve. Serve with a lemon wedge on each edge.