Soak the lentils and beans in plenty of water overnight. Drain them and add to the Instant Pot with 1 litre/4 cups of water and 1 tsp of salt, pressure cook on High for 13-15 minutes, allow for natural pressure release. Drain the lentil and beans but keep 500ml/2 cups of the cooking liquid.
Melt the butter in a deep frying pan and sauté the chopped onion until soft for 5 minutes, then add the garlic and ginger and cook for 30 seconds longer. Then add the tomato passata or crushed tomatoes, smoked paprika, chilli powder and garam masala, stir and cook for a few seconds until it starts to simmer. Add the cooked lentils and beans and 500ml/2 cups of the cooking liquid with a pinch of salt, lower the heat and simmer for 30 minutes, stir once in a while to prevent burning.
Mash some of the lentils and beans with a potato masher to increase the creamy texture, then add in the heavy cream and cook for 5 minutes longer.
Notes
Lentils and beans should be very soft when done in the Instant Pot. When pressure is put on them you should feel no resistance.