Remove the outer leaves from the cauliflower and break into florets, fill a large saucepan with water, season with salt and bring to a rolling boil, drop the cauliflower pieces into the water and cook until tender, drain and rinse under cold water to stop the cooking process
For the sauce - Melt the butter in a saucepan. Stir in the flour and cook for 1-2 minutes. Take the pan off the heat and gradually stir in the milk to get a smooth sauce. Return to the heat and, stirring all the time, bring to the boil. Simmer gently for 8-10 minutes and season with salt and white pepper. Stir in cheese and allow to melt.
Preheat the grill to high. Pop the cooked cauliflower into an ovenproof dish and pour over the cheese sauce, slip under the grill until the cheese sauce is golden and bubbly