Pressure cook the dal till it is almost 90% cooked. Keep the dal aside and wash the cooker and heat with cooking oil.
Splutter mustard, cumin seeds along with broken chilies, curry leaves. Sauté well. Then add the chopped onions, fry till its done. Then, add the tomatoes and cook for a minute.
Then, add the cooked dal, enough water, along with salt and tamarind piece. Cover and pressure cooker for another 2 whistles or till the dal is well cooked.
Check to see if the dal is thin. When you serve the kids, remove the tamarind piece, chilies and mix with well-mashed rice with ghee.