Soak the tamarind in 2 tablespoons boiling water, 5 to 10 minutes. Squeeze the husk and discard the tamarind piece, save the water.
Combine the tamarind water with the flour, chili powder and coriander in a mixing bowl, mix well. Add the cauliflower and coconut milk, stir until cauliflower is coated.
Heat oil in a saucepan. Place the mustard seeds in the oil, when they start popping add the cauliflower mixture. Cover with a lid and simmer until cauliflower is tender, stir occasionally.
