Place 20 whole onions in a mixing bowl, season with salt to taste, and toss thoroughly. Pack them into sterilised jars, fasten muslin across the openings, and rest in a warm or sunny location for 2 days, shaking the jars once daily.
Strain off the liquid from the onions and lay them out on kitchen paper to air-dry for around 2 hours.
In a deep pan, combine 254 g white malt vinegar, 200 g jaggery, 18 g garlic, crushed, the pickling spices, and salt to taste. Bring to the boil and simmer for 10 minutes.
Add the drained onions into the pan and simmer for an additional 5 to 10 minutes. Take the pan off the heat and leave the mixture to cool overnight.
Ladle the onions and spiced syrup into sterilised jars, cover with muslin, and set on a windowsill for 1 week, giving them a daily shake. The pickle is ready to eat after 7 to 10 days.
Use 80% of the weight. Granulated sugar is sweeter by weight, but gives a cleaner, one-dimensional sweetness that lacks jaggery's caramel, molasses depth.
Soak and blend into a paste; use 100% to 120% of the weight. Adds rich, natural, fruity sweetness with complex, dark molasses notes that thicken the gravy.
Use 50% of the weight mixed with equal parts ground coriander and a pinch of ground cinnamon, ground cloves, and ground green cardamom. Sprinkle near the end for a warming finish.
Use 15% to 20% of the weight (about 1 g for every 5 to 6 g fresh cloves). Whisk into sauces; gives a savoury, toasted garlic flavour without raw pungency.