Heat the oven to 100°C/80°C fan/lowest gas setting.
Sprinkle 10g kastori methi onto a foil-lined baking sheet and bake for 20 minutes. Allow to cool completely.
Whizz in a spice grinder with 22g chaat masala, 2g deggi, 1g garam masala and 1g fine sea salt, then decant into an airtight container or jar. Store in a cool, dark cupboard and use within 2 weeks.