1 head cauliflower
1/2 c. mayonnaise
1 tbsp. prepared mustard
1 tbsp. finely chopped onion
8 oz. shredded Cheddar cheese

Cook cauliflower until tender. Place in a rectangular baking dish. Combine mayonnaise, mustard and onion. Spread over cauliflower and top with cheese. Bake at 325 degrees until cheese is melted, about 5 to 10 minutes.