Pour the yoghurt, vanilla and sugar in a bowl. Stir well. Leave the gelatin to swell and melt it in a water bath.
Leave a few of them aside for the very top of the cake, pour the rest into the yoghurt mixture. Lay out plastic wrap along the inside of a cake form.
Arrange the set aside fruits along the bottom. Pour the yoghurt mixture on top. Leave in the fridge for about 3-4 hours to gel. Then take it out, flip over onto suitable platter and remove the plastic wrap.