Heat oil and butter in a pressure cooker and saute onions till lightly browned. Stir in ginger and garlic pastes, tomato paste, chilli powder and salt, and fry for a few seconds.
Add in the chopped tomatoes and cook for a few minutes to combine well. Add in pre-soaked lentils and kidney beans, and enough water to cover them. Pressure cook for 15-20 minutes till lentils are soft and done.
Stir in milk and let it come to a boil.
Garnish with fresh coriander leaves and serve warm.