Put low-fat quark, yoghurt, sugar and milk in a bowl and stir with a whisk for about 3 minutes. Depending on the firmness of the quark and yoghurt, the result will be more solid or fluid - control this via the amount of milk. The result should be a fluffy yogurt quark.
Roughly grate the apples including the skin. Peel the banana and cut into thin slices.
First place the grated apple on a plate, then spread the banana slices on top. Layer the crunchy muesli and finally the yoghurt quark on top.
Tip: Chocolate or crunchy fruit muesli tastes good.