For my money the old Edmonds Cookbook tomato relish is one of the best. I've modified a few ingredients but essentially this is it.
Ingredients
| 2 | Red onions, thinly sliced | 
| 1 ½ kgs | Large ripe tomatoes (Main) | 
| 1 ½ cups | Brown sugar | 
| 1 ½ cups | Malt vinegar | 
| ½ cup | Balsamic vinegar | 
| ¼ cup | Tomato paste | 
| 1 Tbsp | Mustard seeds | 
| 1 tsp | Chilli powder | 
| 1 Tbsp | Curry powder | 
| 1 Tbsp | Turmeric | 
| 2 Tbsp | Plain flour | 
| ¼ cup | Malt vinegar, or white vinegar | 
Directions
- Cut a small cross in the base of each tomato and blanch in boiling water to remove the skins.
- Quarter the tomatoes, mix with the onions, sprinkle with 1½ teaspoons of salt. Leave overnight.
- Drain off the salt the next day and put in a heavy-based pot.
- Brown sugar, malt and balsmic vinegar,m tomatoe paste, mustard seeds and chilli powder all together.
- Bring to a boil then simmer over a low heat for 1½-2 hours, stir often. It should now be quite thick.
- Mix curry powder, turmeric, flour and ¼ cup malt vinegar together.
- Stir this paste into the relish and cook for another 10 minutes.
- Spoon into sterilised jars and seal.