Heat a pressure cooker with oil once its hot add in the karamani / Cowpeas and saute in a low flame for 5 mins and then remove it and set aside. In the same cooker add in mustard seeds and cumin seeds let it splutter and then add in the curry leaves.
Next add in the chopped onion and garlic, saute till its glossy and then add in the tomatoes, cook till it turn mushy.
Mean while in a blender add in the coconut and fennel seeds, add little water and blend it to a fine paste. Next add in the sautéed karamani in the cooker.
Mix well and then add in the Chilli powder, Coriander powder and Turmeric powder. Next add in the required Salt.
Soak tamarind in water and extract the pulp and add the tamarind pulp to the Kuzhambu. Next add in the ground coconut fennel seeds paste along with the required Salt.
Add salt and spice if required. Close the cooker, once the steam comes more put on the whistle. In a medium low flame cook for 5 whistles, wait till the pressure subsides on its own and then open the cooker. Serve hot with rice.