Cook the vegetables separately in salted water for approx. 10 mins. each so that they are firm to the bite, place in the prepared dish in alternate layers.
Sauce & cheese topping
Transfer the milk, single cream, flour and bouillon powder to a shaker and shake well, pour over the vegetables. Mix the parsley with the breadcrumbs and grated cheese, sprinkle over the gratin.
Bake for approx. 20 mins. in the centre of an oven preheated to 180 °C (until a cheese crust forms).