Put the coriander seeds, cumin seeds, mustard seeds and fennel seeds into a spice grinder and grind to a powder.
Transfer to mini food processor and add the garlic, chili, turmeric and coconut and blend to a paste. Add 1/4 cup of water and blend again.
The Squid
Heat the oil in a sturdy wok over a medium heat, add the cumin seeds and fry for 30 seconds until they begin to pop, then stir in the onion and serrano pepper and fry for 3 minutes. Stir frequently so it doesn't burn.
Add the garlic and ginger and fry for a minute, then stir in the squid, the masala paste, chilli powder, tomato, salt and 1/3 cup water and simmer for 2–3 minutes, or until the squid is cooked but still tender.
Stir in the tamarind and Splenda.
Notes
** I didn't have any Kashmiri chili powder, but I did have have dried Kashmiri chilies. I threw about 4, with the seeds removed, into a spice grinder and whizzed until powder.Adapted from Rick Stein's India