Slowly add cold milk, little by little, constantly stirring so that there are no lumps.
When sauce is thickened, add chicken meat, chicken stock and vegetables. Season the mixture. Transfer into buttered round 7" / 18 cm diameter, deep dish (4 cups / 0.9 liters volume).
Bake for 35-45 minutes in 350 F / 175 C oven or until topping is golden.