For the yoghurt mousse, mix the yoghurt with the powdered sugar in a bowl. Meanwhile, soak the four gelatine sheets in cold water. Pour some of the yoghurt into a frying pan and gently warm it. Squeeze the water out of the gelatine sheets and dissolve them in the warm yoghurt. Pour the warm yoghurt back into the bowl with the remaining yoghurt. Stir well. Whisk the cream until stuff, then gently fold it into the yoghurt. Pour the mass into a rectangular tray and leave it to set in the refrigerator.
For the raspberry jelly, boil the raspberries in a saucepan with sugar and lemon juice. Strain the raspberries through a sieve to remove the seeds.
Soak the gelatine in cold water. Squeeze the water out of the three gelatine sheets and dissolve them in the warm raspberries. Put a small quantity of the raspberry sauce into a bowl and set it aside. Pour the remaining sauce over the set yoghurt mousse and return it to the refrigerator.
Squeeze the water out of the last gelatine sheet, dissolve it in the remaining warm raspberry sauce and pour the sauce into a small, rectangular container with an even base. Refrigerate this container, too.
To serve, take the yoghurt mousse out of the refrigerator, cut it into squares and arrange them on the plates. Cut the raspberry jelly into small squares, too, and arrange them on the plates decoratively. Garnish with berries and mint.
