Put moong dal, masoor dal, turmeric powder, red chilli powder, salt, oil and 3 cups water in a pressure cooker.
Pressure cook the dal for 1 vessel. Till then chop the tomato and slice the green chillies for tadka.
Allow it to cool.
Open the pressure cooker and stir the dal properly.
Now prepare the tadka - put 2 tablespoon oil, grated ginger, cumin seeds, 3 or 4 sliced green chillies and 1 large chopped tomato into a pan. Cook for 4-5 minutes.
Add 1 whole red chilli in the tadka. Again cook for 3-4 minutes on low flame.
Now add garam masala powder and coriander powder. Mix the tadka properly.
Mix the tadka into dal.
Add tamarind juice in the end. Mix the dal properly.
Khatti dal is ready to. Serve it hot as a dal rice or with chapati/paratha.