I love cauliflower and this is my ultimate happy dish.  Don't throw the leaves or core away.  Wash the leaves and cook them according to this recipe or put to one side for another day.  The central core is nice cut into batons and put into a stir fry.

Ingredients
1 large cauliflower (roughly 650g)
175g mature cheddar, grated
75g gruyère grated
125g parmesan, grated
700ml full-fat milk
50g butter
50g plain flour
1 tsp Dijon mustard
50g breadcrumbs
15g crispy onions or shallots (optional)

Method
Preheat the oven to 190c. 

Put the leaves and florets into an oven dish and drizzle with the oil.  Season with salt and pepper and scatter over about 50g of the Parmesan.  Put into the oven for around 30 minutes until softened and beginning to caramelise.

15 minutes into the cauliflower cooking, carefully turn them over and return them to the pan. Meanwhile melt the butter in a saucepan over a medium high heat and then stir in the flour and cook out for 1 minute, stirring constantly.  Take off the heat and gradually add the milk and continually whisk until smooth.  Put back on the heat and cook for 5 minutes or so, this will make the sauce go beautifully glossy. 

Mix the cheeses together and put to one side.  Turn off the heat and add the mustard and stir again then add three quarters of the cheese stirring until melted.  Check for seasoning and add more salt if needed and ½ tsp of ground white pepper and stir through.  

Put the cauliflower into the cheese sauce and carefully stir to ensure all of the cauliflower is covered.  Mix the remaining cheese with the breadcrumbs and crispy onions if using and scatter over the top.  Put into the oven for 20-30 minutes until bubbling and golden.