Onam special recipe: Vegetable sambar

Ingredients:
1 cup tuvar or arhar dal
2 cups mixed vegetables (okra, french beans, potatoes, onions, brinjals, tomatoes)
1 tbsp seedless tamarind (soaked in 1/2 cup water)
1 tbsp sambar powder
1/2 tsp red chilli powder
1/2 tsp turmeric powder
A pinch of hing
5 cups water 
salt as required

For tempering (tadka/chaunk) of sambar
3 dry red chillies
1 tsp mustard seeds/rai
1/4 tsp fenugreek seeds (optional)
A pinch or two of hing
2 to 3 cloves garlic - crushed lightly with the peels (optional)
12 to 15 curry leaves

Method:
First soak the tamarind in warm water for 30 mins. Rinse the dal in water well.
Boil the dal in 3 cups water in the pressure cooker and wait for 8-9 whistles on medium to high flame. the dal should become soft. Once the pressure settles down on its own, remove the lid of the cooker.
Now add the chopped veggies, turmeric powder, red chili powder, hing and salt. Add 2 cups water and stir well. Pressure cook again for 1 whistle on medium flame. Once the pressure settles down on its own, remove the lid.
Add the sambar powder and tamarind pulp. If the consistency of sambar is thick, then add some water or else keep the cooker on the stove and and then cook the sambar for 10-12 minutes on a low flame.
Keep on stirring at intervals. 
In a small pan, heat oil. Crackle the mustard seeds first.Then add the fenugreek seeds, garlic, red chilies, hing and curry leaves.Fry it till the garlic turns a light brown. Pour the whole tempering in the steaming hot sambar. Close with a lid so that the flavors infuse.
Later stir and then serve the vegetable sambar.