Mix together the oats, 100g of the yoghurt, coffee, 1tbsp of the granulated sweetener and vanilla extract.
Place this mixture in the bottom of a Kilner jar (the jar should be able to hold up to 350ml).
In a clean bowl, mix together the remaining yoghurt, quark, vanilla extract, chia seeds and remaining granulated sweetener. Beat it well to remove any lumps.
Pour this mixture on top of the oat mixture, close the lid and refrigerate overnight.