Bring the milk and butter to the boil in a saucepan, stir in the flour until the dough loosens from the saucepan, stir a little cool. Gradually stir the egg yolks into the batter. Mix in the quark, chives and the boiled eggs. Season with salt and pepper and fold in the egg whites.
Grease and flour a casserole dish and fill 2/3 with the mixture. Bake in the preheated oven at 180 ° C top / bottom heat for approx. 18 minutes.
For the sauce, mix the sour cream with parsley and dill and season with mustard, salt and pepper.
Tip: Always open the oven door carefully when making a casserole.