In a small bowl, mix together the tomato paste and 1/2 cup milk until smooth.
In a large skillet, heat the olive oil. Sauté the cumin seeds until they just start to brown, about 1 minute. Add the onion, garlic and ginger, and sauté 1 to 2 minutes.
Add the chili powder, coriander, garam masala, cayenne pepper, butter, the tomato paste and milk mixture, and another 1/2 cup milk. Add the beans and lentils and the kosher salt.
Heat and stir, gradually adding the remainder of the milk (1 1/2 cups, or more) over a few minutes until a thick sauce forms.