Peel the rind off the lemons and put in the bowl of the food processor and pulse chop then put in the large saucepan.
Juice the lemons, pour into a measuring jug and set aside.
Roughly chop the onions then pulse chop in the food processor and add to the large saucepan.
Roughly chop the chillies then pulse chop in the food processor and add to the large saucepan.
Grate the ginger and add to the large saucepan.
Add the sugar and salt to the large saucepan.
Add enough white vinegar to the lemon juice to get 1 litre of liquid and add this to the large saucepan.
Give everything a good stir with a wooden spoon over medium-high heat until it boils. Reduce the heat to a simmer and cook until it is thick and syrupy. This will take 2 to 4 hours. Stir the mixture regularly to avoid it sticking to the bottom of the pan and burning.