Drain the lentils and place in a saucepan. Add 1 1/2 litres water and bring to a simmer. Simmer 1 hour until lentils are cooked but not mushy.
Add the garlic ginger paste, salt and chilli powder then simmer a further 10 minutes. Reduce heat and add tomato paste and butter. Simmer 15 minutes, stirring. Stir in the garam masala, sugar and cream and serve immediately.