Heat the butter in a small pan over a gentle heat until foaming. Add the flour and cook, stirring constantly for 2 minutes. Add the milk and stir until blended. Simmer for 15 - 20 minutes.

Meanwhile, boil or steam the cauliflower for 15 - 20 minutes until just tender.

Heat the oil in a pan and fry the onion until golden. Grill the bacon until crisp. Chop.

Drain the cauliflower very well and put into a shallow ovenproof dish. Stir the onion and 2 oz (50 g) of the cheese into the white sauce. Stir well.

Pour over the cauliflower and top with the bacon and remaining cheese. Grill until golden.