Whisk the cornstarch with the vanilla sugar in the milk without lumps and bring to the boil in a saucepan while stirring. Remove the saucepan from the plate and quickly stir in the egg yolks. I always use a whisk for everything. Let the pudding cool down a bit.
Meanwhile let the chia seeds soak in the milk. Then mix the chia seed milk with the quark and sugar and stir in the pudding.
Pour into glasses and serve with fruit or compote to taste.