More urundai kuzhambu(Steamed lentil balls in yogurt gravy)

A gravy made of buttermilk is standard fare in any South Indian home. It goes by the name of more kuzhambu in Tamil Nadu, moru kari in Kerala and majjige huli in Karnataka. The usual version that I make with ripe plantain or colocasia or ash gourd is posted here.
This version is made using steamed balls of tuar dal. I first tasted this at a restaurant in Chennai and quite liked the aroma and the taste of it. Today, with the help of Mallika Badrinath's recipe from her book Classic Lunch Recipes, I have been able to recreate a remembered taste.

What you need:
For the urundai/koftas
Tuar dal - 1/2 cup(scant)
Whole white urad - 1 tbsp
Green chillies - 2 or 3(adjust to taste)
Onion - 1 small, chopped very fine
Chopped corriander leaves - a few
Cumin seeds - 1/2 tsp
Salt - to taste (use a little less than you normally would as the gravy too has salt)

For the kuzhambu/gravy
Sour thick curd - 2 cups (beaten lightly to break up lumps)
Turmeric powder - 1/2 tsp
Salt
Grind together:
Fresh grated coconut - 1/4 cup
Green chillies - 2 or 3
Coriander seeds - 1.5 tsp
Cumin seeds - 1/2 tsp
Tuar dal - 1 tbsp
For tempering:
Oil - 1 tsp
Mustard seeds - 1/2 tsp
Red chillie - 1, broken
Methi seeds - 1/4 tsp
Curry leaves - a few

To make koftas/urundai:
Soak the dals together for an hour. Drain all the water. Add in all the other ingredients except onion and corrinder. Grind to a coarse paste without adding any water. Mix in the chopped onions and corrainder. Shape into lemon sized balls. Grease an idli plate and stem for 8-10 minutes. Set aside the balls to cool.

To make kuzhambu:
Soak all the ingredients listed under Grind together, except coconut in just enough water to cover for at least 30 minutes. Add coconut and grind to a smooth paste.
Transfer this to a pan. Add 1/2 cup of water, salt, turmeric powder and let it boil for a few minutes. Add the whipped curd and boil some more. Just before removing from fire, add the steamed koftas and boil for a minute or two.
Heat the tempering ingredients until the mustard seeds pop. Pour this over the kuzhambu.
Enjoy with rice/idli/dosa.
This tastes even better the next day after the flavours have blended together well.
Today is Day 3 or Blogging Marathon #7, and this is my post under the theme Cooking from cookbooks. Check out the blogging marathon page to see what my fellow marathoners are cooking.