Break the cauliflower apart into smallish florets then put them into a steamer.
Steam cook the cauliflower, which should take about 10 - 15 minutes once the water is starting to boil.
Prepare the sauce by melting butter on medium heat then add the grated cheese, mustard and cream. Add salt, pepper or any favorite spice or herbs if desired. Mind that mature cheddar is salty.
Mix everything well together.
Place the cauliflowers into an oven proof dish and pour the sauce over them. Ideally the sauce should cover all the florets.
Place the cauliflowers into a 390°F / 200°C preheated oven until golden brown spots start to appear on top for about 15 - 20 minutes.