Step 1

Preheat the oven to 200C/180C Fan/Gas 6.

Step 2

A third fill a large saucepan with water and bring to the boil. Add the cauliflower and/or broccoli and return to the boil. Once it's boiling, remove from the heat and drain well.

Step 3

Melt the butter in a large saucepan and gently fry the onion for 3–4 minutes, or until softened but not coloured. Stir in the flour and cook for around 30 seconds before slowly adding the milk a little at a time. Cook for 4–5 minutes, or until thickened, stirring constantly. Add two-thirds of the cheese, the cooked gammon or ham and the mustard, if using. Simmer very gently for 1–2 minutes, or until the cheese melts. Season to taste with salt and pepper.

Step 4

Scatter the vegetables over a shallow ovenproof dish and pour the sauce over the top. Sprinkle with the remaining cheese.

Step 5

Bake for around 20 minutes, or until golden brown on top and bubbling. Serve immediately.