Wash the dal and soak in 2 cups water
Clean and cut drumsticks into 1 inch peices
Grind 1 sliced onion, all red chillies and cumin to a smooth paste with little water
Cut another onion into thick roundels
Meanwhile Pressure cook the dal for 3 whistles. Cool completely.
Now grind the dal and the masala paste together
Heat 2 tbsps oil in a deep sauce pan. Add mustard seeds. Let it splutter
Now add curry leaves and garlic. Saute for few seconds. Add onion roundels and saute.
Add the chopped drumsticks and saute till slightly browned.
Now add the dal paste. Water and salt to season.
Let it come to a boil. Lower the gas. Cover partially and simmer for 10 minutes.
The curry will be thick. If you want it more thin then can add some water and simmer for few more seconds.