If you are using dried beans soak them for 2 to 3hrs or overnight.
If your are using tamarind soak it water and extract the juice. If you are using the paste, mix it 1 cup of water and set aside.
Pressure cook the ½ cup of toor dal with 2 cups of water and ½ tsp of turmeric powder.
Let it cool down and mash it well.
Pressure cook beans for 2 whistles or you can microwave them.
Cut the bitter gourd into two halves and remove all the seeds and chop them.
Microwave them for about 5 minutes and make sure they are al-dente and not mushy.
Dry roast all the ingredients given under roast and grind and grind them by adding ½ cup of water and set aside.
Method
Heat the kadai or the heavy bottom vessel and add oil.
Once the oil is hot, add the mustard seeds, methi seeds and hing.
As they start to splutter, add the microwaved bitter gourd and black eyed peas.
Now add the tamarind water, salt and mix well. Let it simmer.
As it starts to simmer, add the ground masala and and mix well.
Let it simmer again for couple of minutes and then add the mashed toor dal mixture.
Check for salt at this stage and if required add more.
Mix well and let it cook for 5 more minutes and turn of the heat. Pitlai is comparatively thicker than sambhar. So let it simmer till it thickens.
Finally add the cilantro and curry leaves.
Notes
Bitter gourd can be replaced with cluster beans or brinjal.
Similarly black eyed peas can be replaced with brown chick peas or garbanzo beans or beans of your choice.
My MIL adds 1 tsp of sambar powder and that gives it more darker color and also adds spice. You can adjust the spice level either by adding more red chillies or sambar powder.