Step 1

Sterilise the jars. Wash in very hot water or on the hot cycle of a dishwasher. Preheat the oven to 160C/325F/Gas Place the jars upside down on a baking tray and dry in the oven for 10-15 minutes.

Step 2

Heat the red onion and chopped tomatoes in a large heavy-based saucepan over a low heat.

Step 3

Add the chillies, ginger, star anise, vinegar and sugar. Bring the mixture to the boil, then simmer for about 30 minutes, or until very thick and you can draw a wooden spoon across the base of the pan so that it leaves a channel behind it that does not immediately fill with liquid.

Step 4

Add the fish sauce and cook for 2-3 more minutes, then spoon into sterilised jars.