Roast horse gram in a dry pan and soak it for 30 mins. Now take it in a cooker, cover with water and cook for 8 to 10 whistle till it is cooked. Now drain it and add it to a blender. Puree till smooth, set aside. Reserve the cooking liquid as well.
Take grinding ingredients in a blender and puree till smooth, set aside.
Now heat oil in a pan, add in mustard, urad dal, asafoetida and let them sizzle. Add in turmeric powder and mix well.
Add in the horse gram cooking water and the ground horse gram mix. Mix well.
Add in tamarind and salt and boil it for 5 mins or so.