Bring daal, salt and 4 cups water to boil, lower heat and simmer 45 minutes till daal feels soft when pressed between finger tips. Strain daal and place back in cooking pot and reserve the liquid.
In fry pan heat 3 Tbsp oil put in the cumin till the crakkling stops, add chopped onion and fry till golden, add the ginger and fry for 15 seconds. Pour into daal and add 1 1/4 cups reserved liquid and simmer for 10 minutes stirring gently to prevent sticking to bottom of pan. Taste for salt and more if not enough.
Add the cream and allow to simmer for 2 minutes till heated through. Stir gently as you simmer cream.
Can be eaten with chippattis (pita bread), naan, or rice and sliced tomatoes and onions sprinkled with salt and vinager.