Break the cauliflower and broccoli into florets and cook in lightlysalted, boiling water for 10 minutes until just tender. Drain well and transfer to a flameproof dish.
Mix together the yogurt, grated cheese and mustard, then season the mixture with pepper and spoon over the cauliflower and broccoli.
Sprinkle the bread crumbs over the top and place under a moderately hot grill until golden brown. Serve hot.Servings: 4