Toast the chiles in a dry skillet over medium heat for 30 seconds, shaking the pan to move around. Add the cassia bark (cinnamon stick), cardamom and peppercorns and toast another 30 seconds.
Next add the coriander, cumin, fenugreek and mustard seeds, toast for 1 minute.
Transfer the spices to a plate and let cool completely.
Transfer to a spice grinder. Add the dried curry leaves and turmeric. Grind to a fine powder.
Store in an airtight container and use within three months for maximum freshness.