Line the gratin dish with baking paper.
Mix the yoghurt and apple jelly in a bowl, transfer to the prepared dish.
Mash the raspberries with a fork, spread on top of the yoghurt, create a marble effect using the fork.
Spread the muesli on top of the yoghurt.Freeze the yoghurt for approx. 4 hrs.
Remove the frozen yoghurt from the dish. Break into pieces, serve immediately.