Step #1 Place the sliced tomatoes & onion In a large-ish dish or colander & cover with salt.
Step #2 Leave for a few hrs to drain off the liquid.
Step #3 Put the tomatoes & onions in a saucepan & add three quarters of the malt vinegar & boil for five mins.
Step #4 Stir in the sugar.
Step #5 Meanwhile mix the flour, curry power & cayenne pepper, mustard powder, if using, into a smooth paste with the remaining malt vinegar.
Step #6 Add the paste to the pan & let simmer carefully for one to one & a half hrs.
Step #7 To test whether the chutney has reached the required consistency, draw a wooden spoon through the mixture: it should leave a clean path with no free liquid showing.
Step #8 Decant into warm jars.
Step #9 The finished chutney mellows with keeping & should be kept for at least 6-8 weeks before eating.