Preheat oven to 190C. Grease an ovenproof dish and bring a double boiler saucepan to the boil.
Trim the cauliflower head and break or slice into florets. Cook in a steamer for 2 minutes until just tender, then tip cauliflower pieces into the greased dish
Melt butter in a heavy-based saucepan and stir in flour, cooking for a minute. Remove pan from the heat and gradually add the milk, stirring constantly so it is smooth.
When all the milk is incorporated, return pan to the heat, and bring to the boil stirring constantly. Reduce heat and simmer for 2 minutes.
Remove from heat and stir in half of the cheese and the nutmeg until the cheese is melted through the sauce. Pour sauce over the cauliflower, then top with remaining cheese.
Bake in the oven for 20 minutes, or until golden.
Sprinkle with fresh Italian parsley and serve as a side dish, or as a tasty lunch for two.