Put the cauliflower in a pan of boiling water and simmer for 5-6 minutes.
In a bowl, mix together the creme fraiche, ¾ of the cheese and mustard (if using)
Drain the cauliflower well and put in a bowl with the creme fraiche mixture and mix well.
Put in a baking dish and top with the rest of the cheese.
Put in a preheated oven at 190°C/375°F/Gas 5 and bake for 20 minutes.
Add some extra flavour with a spoonful of mustard and a pinch of nutmeg.
You could add some panko breadcrumbs on top to make this extra crispy.
You can also use frozen cauliflower to make this cauliflower cheese. Just cook it according to the packet instructions.
Make sure you don't overcook the cauliflower. You want it to still be a little tender when you put a knife in to it (about 5-6 minutes par-boiled). If it gets too mushy, then it will be watery when it goes in the oven and can cause the sauce to split. You will need to make sure it is drained properly too.
Drain the cauliflower well, so you don't end up with a watery dish.
Leftovers are really good on a baked potato.
If you want to add a little freshness, then a sprinkling of fresh chopped chives or parsley goes well with this.