I had a whole pile of peppers and tomatoes left over from a market visit a week ago so decided to make a relish. Having never attempted this feat before I enlisted the help of my mother over the telephone - her advice was two fold: 1) make sure you use enough vinegar and sugar, and in equal parts and 2) make sure you salt the tomatoes and onions thoroughly to remove moisture.
I started with about 800g of fresh tomatoes and two large red onions, slicing the onions and chopping the tomatoes into 2cm chunks. In a non-reactive bowl I salted with 2 tablespoons of salt. Leave for 4 hours.
Chop 1 kg of sweet peppers (this yields about 800g) into squares and the zest of 1 lemon add 1 teaspoon each crushed black pepper corns, chili flakes, cumin seeds, crushed coriander seeds and crushed fennel seeds. I used much too much chili and forgot to crush the pepper, coriander and fennel making for little explosions of pungency.
Add all of these to a large pot and add 4 cups each white sugar and white wine vinegar. Bring to a simmer and leave on low. After two hours add 4 peeled, cored and finely chopped green apples. (I had not originally planned to do this but I had much too much liquid and the mixture was super spicy - you could choose to add 1-2 cups less vinegar and sugar if you chose too but I liked the end result). Simmer for another two hours. The mixture should set when it comes in contact with a cold surface.
Sterilize jars by rinsing first and then putting in oven at 180 degrees for 20 minutes and likewise, boil lids. Fill each jar and seal immediately - keep for 3 months before use. With apples this recipe yielded six 300ml jars - without it would probably yield three.