Soak 2 tbsp chana dal, 1 tsp tamarind separately in two bowls for 30 mins to 1 hour.
Extract tamarind juice. Cut bitter gourd into cubes or thin slices, how ever you like it. (remove seeds)
Pressure cook 2 tbsp moong dal, with the soaked chana dal in one container. In another container, add cut bitter gourd with tamarind juice (1 cup), 1 tsp sambar powder, 1/4 tsp turmeric powder, 1/2 the salt. For 4 whistles.
Meanwhile, heat a pan with 2 tsp oil, add 1 tbsp chana dal, 1 tsp urad dal, 1 tsp coriander seeds, 5 red chillies, 1/8 tsp asafoetida.
Roast in medium flame until dals turn crisp and golden. Transfer to a plate to cool down.
Grind the roasted items with 1/4 cup grated coconut, 1/2 cup water to a paste.
Once the dal and bitter gourd are cooked, transfer both to a heavy bottomed vessel.
Adjust salt and water. Bring to boil.
Add ground paste and mix well. Adjust water if needed. Bring to boil. Keep stirring often.
Switch off the stove. Temper with mustard, curry leaves and mix it with pitlai.