First, sterilise a 1½ litre jar (or smaller jars). Put the beans, mango, squash, onion and garlic in a large heatproof bowl.
Gently toast all the spices for the base in a nonstick frying pan until fragrant, then tip into a spice grinder and blitz to a fine powder.
Add the ground spices and a tablespoon of salt to the vegetable bowl, then mix well to combine.
Put all the ingredients for the pickling liquid in a blender, add 100ml cold water, then blitz smooth.
Pour the mix into a small saucepan, bring up to a gentle boil, then cook, whisking constantly, for about 10 minutes, until thickened and no longer chalky.
While the liquid is still hot, pour it over the vegetables and toss to combine.
For the temper, put a medium saucepan on a medium-high heat, then add the oil, curry leaves, whole green chillies and mustard seeds.
When the oil begins to bubble and smell fragrant, add the cumin seeds and cook for another minute.
Take the pan off the heat, immediately pour the temper over the vegetables and mix again to combine.
Pack the atchar mix tightly into the sterilised jar (or jars), making sure it’s completely submerged in liquid, then put in the fridge or a cupboard and leave for at least three days before digging in.
