Bring water to the boil in a frypan on the highest setting. Add the cummin, coriander, paprika, black mustard seeds and turmeric. Boil ferociously for a good five minutes, adding boiling water if the mixture begins to dry out too much. Add the garlic, ginger, chillies and onions with a little more water and continue on a high heat. Add the base of the cauliflower and any green stalks and simmer covered till soft. Add the cauliflower florets and baste in the spices (a little more water may be needed). Add the tomatoes, stock, salt and pepper and leave simmering covered for about 15 minutes. Add the sweet corn (optional, un-authentic, but what the hell) and then the tomato puree to thicken. Serve with brown basmati rice or home made chappatis (which my wife makes so don't ask me how :-).