Boil the cauliflower in salted water until al dente, drain and place in a greased casserole dish.
Melt the butter in a saucepan and stir in the flour. Carefully add the milk with a whisk, let it get hot, then add the cheese. When the cheese is melted, season with mustard, nutmeg and Worcestershire sauce.
Pour the sauce over the cauliflower and bake in the oven at approx. 180 degrees until it is golden brown. Baked potatoes taste best with it.