Preheat the oven to 200C. Bring water to a boil and cook the cauliflower for 5 minutes.
Drain the cauliflower and then place it in an oven safe dish.
Simmer milk, butter and flour in a saucepan until it starts to simmer. Whisk for 2 minutes until the sauce becomes thick. Turn off the heat and stir in 1/2 of the cheese.
Then pour over the cauliflower and sprinkle the rest of the cheese on top. Bake for 20 minutes or until its golden brown.