Preheat your oven to 220ºC/200ºC fan/gas mark 7/425ºF.
Chop your cauliflower into small florets and put into a large saucepan. Cover with cold water, a pinch of salt and the bay leaves and bring to the boil over medium heat. Drain the cauliflower once boiled, refresh with cold water then leave to drain completely. Then spread evenly into an ovenproof dish.
Make the cheese sauce! Melt the butter in a saucepan, then whisk in the mustard and flour and cook over low heat for 5 minutes.
Take the pan off the heat and add the milk and single cream and mix. Put the pan back onto the low heat and stir until the sauce becomes thicker and is bubbling gently.
Sprinkle Red Leicester cheese into the sauce, leaving a handful for the top, and stir until the cheese melts. Season if necessary.
Pour the cheese sauce over the cauliflower and sprinkle the remainder of the cheese over the top.
Bake in the oven for about 20 minutes or until the cheese on top is slightly brown and bubbling.