Remove leaves and trim base from cauliflower. Wash and cook whole in boiling salted water 15 - 20 minutes, or until tender. Drain and place in ungreased shallow baking dish, sprinkle with salt. Mix mayonnaise and prepared mustard; spread over cauliflower. Top with cheese; bake at 350°F for about 10 minutes, or until cheese is melted. This recipe is also good for broccoli, or you can place 1/2 and 1/2 in the same dish.