In a wide bowl, combine 225 g chickpea flour, the flour spices, 4.2 g granulated sugar, and salt to taste.
Warm 27 g vegetable oil in a deep, heavy pan over medium heat, then tip in 3 tsp mustard seeds and the tempering spices, stirring for about 1 minute until fragrant.
Increase the heat to high, add 6 prepared green bell peppers, and stir-fry for a few minutes until partially tender.
Lower the heat to medium and scatter in the seasoned chickpea flour mixture, tossing thoroughly to ensure the peppers are fully coated.
Cook for another 5 minutes, turning occasionally, until the coating is golden and crisp, then finish with 2 tsp chopped coriander to garnish.
For crisping batters or binding cutlets: use 50% to 60% of the weight. Produces a very crisp shell but lacks the earthy, roasted nutty flavour of besan.
Steep a tiny pinch (0.1 g per 2 g turmeric) in 2 tbsp warm water; use to match the rich golden hue. Contributes an aristocratic, honeyed floral flavour rather than earthy bitterness.
Use the same weight. The seeds are smaller and hotter; fry in hot oil until they pop, about 20–30 seconds, and reduce the heat if they darken too fast. The dish will be a little sharper.
Use 70% of the weight of whole seed, added with the other ground spices rather than fried whole. You lose the popping texture and the heat comes through more evenly.