50g 2 tbsp spoons breadcrumbs made from slightly stale bread
Preheat the oven to 200C/hot. Cut the cauliflower into large florets and add to a large pan of boiling water. Simmer until just tender. Drain and put in an ovenproof dish.
Melt the butter in a medium-sized pan. Remove from the heat and stir in the flour. Stir over a low heat for 2 minutes.
Remove from the heat and gradually whisk in the milk.
Add the cayenne and mustard powder and bring to the boil, whisking all the time. Mix the cornflour with 2tbsp water to form a smooth paste, and stir in. Simmer for 2 minutes, stirring occasionally. Remove from the heat.
Set aside 25g of the Cheddar and add the rest to the sauce with the Parmesan. Season to taste. Pour the sauce over the hot cauliflower and sprinkle with the breadcrumbs and remaining Cheddar. Cook in the oven for 10 minutes.