Preheat the oven to 180 C Fan. Steam the cauliflower over boiling water for 5 minutes, until just softening. Remove and set aside to cool slightly.
Put the butter into a 24cm round casserole pan or ovenproof dish of a similar size and place on a medium heat. Add the onion and saute for 8 minutes, until soft and golden.
Add the cumin seeds, curry powder, mustard powder and chillies and cook for 4 minutes, stirring occasionally. Add the mustard seeds, cook for another minute then pour in the cream.
Next add 100 g of the cheddar and 1/2 tsp salt and simmer for 2-3 minutes until slightly thickened. Add the cauliflower, stir gently and simmer for another minute before removing from the heat.
Place the remaining 20g of cheddar in a bowl and add the breadcrumbs and parsley. Mix, then sprinkle over the cauliflower. Wipe the top inside edge of the pan clean to prevent any liquid burning.
Put into the oven and bake for 8 minutes until the sauce is bubbling and the cauliflower is hot. Turn the grill to high and keep the pan underneath for 4 minutes or until the top is golden and crisp, being careful not to burn.
Remove from the grill and allow to cool for about 5 minutes before serving.