Wash the plantains, remove the skin carefully (so as to not damage the flesh) and cut into medium size cubes and soak in water (to avoid them from turning black). If you are using tamarind pulp, soak it in a little water to extract the juice.
On a hot tawa/skillet, roast the whole red chillies, coriander seeds and coconut one by one. Allow to cool and using a little water grind them along with the rest of the ingredients mentioned under 'For the masala' to a fine paste. Retain the water from the mixie
In a pan, bring 2 cups of water to a boil, add the tamarind water (or tamarind paste) and salt to taste and cook the plantain cubes till tender but not mushy.
Add the ground masala, mix gently and add a little of the water from the mixie. Adjust consistency of the curry as desired (if you wish to eat it with chapathis, then keep a semi dry consistency). Simmer for 2 minutes. Adjust salt to taste (remember that salt was added while precooking the plantain)
In another pan, heat the oil for seasoning. Toss in the mustard and when it stops spluttering add the curry leaves, broken red chilli, crushed garlic and finally add the coriander and cumin powders - quickly toss the ingredients in the hot oil using a spoon and remove from the flame immediately before the powders burn. Add this seasoning to the curry and cover the pan immediately so as to retain the aromas of the seasoning. Turn off the flame.