Preheat the oven to gas 6, 200°C, fan 180°C.
Remove outer leaves from cauliflower and chop into florets.
Cook florets in boiling water for 5 mins.
Melt butter in a pan, stir in flour to make a roux base.
Gradually add milk, stirring constantly.
Add Cheddar cheese, English mustard, and season.
Pour cheese sauce into a baking dish, add cauliflower, cover with sauce, and top with Cheddar.
Bake for 20 mins until golden brown and bubbly.
