1. Preheat the oven to 375°F (190°C). Trim away the leaves from the cauliflower, then cut off the florets from the main stem. Cut the broccoli florets away from the stem. Blanch both the cauliflower and broccoli florets in a large pot of boiling water for 1 minute, then drain thoroughly.

2. Put the scallions into the same pot. Mix the cornstarch with a little of the milk in a large heatproof bowl to make a smooth paste. Pour the rest of the milk into the pot with the scallions and bring the milk to a boil. Stir half of the hot milk into the bowl with the cornstarch paste, mix well, thenreturn the entire mixture to the pot. Bring the mixture to a boil, stirring frequently, to make a smooth white sauce.

3. Remove the white sauce from the heat and stir in the grated cheese, beaten egg and half the breadcrumbs. Stir in the blanched vegetables and season to taste with freshly ground black pepper.

4. Transfer the vegetable mixture to a greased, ovenproof baking dish or gratin dish. Scatter the rest of the breadcrumbs and the walnuts over the top of the vegetables, then bake for about 20 minutes until golden. Serve immediately.

Variations: Pine nuts are a good alternative to walnuts. You could also arrange 100 grams (31⁄2 oz) halved cherry tomatoes, cut side up, on top of the vegetables in the sauce, before adding the breadcrumbs and nuts.

Serves 4

Preparation time: 20 minutes

Cooking time: 25 minutes

Per serving: 378 calories, 14 g fat (5 g saturated), 24 g protein, 36 g carbohydrate, 7 g fibre