Heat the oil in a large saucepan over a medium heat and cook the shallots for 5-6 mins until softened and lightly golden. Add the garlic, fennel seeds and chillies. Cook for 2-3 mins until fragrant.

Add the tomatoes, sugar and vinegar, stir well, then bring to the boil. Reduce the heat to a simmer and cook for 45 mins-1 hr, or until the mixture has thickened and become sticky, and a spatula leaves a clear path when drawn through it. Transfer to a sterilised 500ml jar (find out how to sterilise jars) and leave to cool completely. Will keep unopened for up to a year in a cool, dry place.