1 large red onion, peeled and roughly chopped
1/2 bulb fennel, trimmed and roughly chopped
1 stick celery, trimmed and roughly chopped
Thumb-sized piece fresh ginger, peeled and roughly chopped
2 cloves garlic, peeled and sliced
1/2 a fresh red chili, deseeded and finely chopped
Bunch fresh basil, leaves picked, stalks chopped
1 tablespoon coriander seeds
1 teaspoon freshly ground black pepper
1 pound amazing cherry or plum tomatoes, halved plus 1 pound canned plum tomatoes, chopped or 2 pounds yellow, orange or green tomatoes, chopped
3/4 cup plus 2 tablespoons red wine vinegar
1/3 cup soft brown sugar
Place all the vegetables in a large heavy-bottomed saucepan with a big splash of olive oil and the ginger, garlic, chili, basil stalks, coriander seeds and cloves. Season with the pepper and a good pinch of salt.
Cook gently over a low heat for 10 to 15 minutes until softened, stirring every so often. Add all the tomatoes and 1 1/2 cups of cold water. Bring to the boil and simmer gently until the sauce reduces by half.
Add the basil leaves, then whiz the sauce in a food processor or with a hand blender and push it through a sieve twice, to make it smooth and shiny. Put the sauce into a clean pan and add the vinegar and the sugar. Place the sauce on the heat and simmer until it reduces and thickens to the consistency of tomato ketchup. At this point, correct the seasoning to taste.
Spoon the ketchup through a sterilized funnel into sterilized bottles, then seal tightly and place in a cool dark place or the refrigerator until needed - it should keep for 6 months.