clean and wash the beans. Put in a deep saucepan with the turmeric and water, and bring to a boil. lower the heat and cook, partially covered, for 1 1/2 hours.
add the spinach to the beans, mix thoroughly until the greens wilt, and continue cooking, covered, for an additional 15 to 20 minutes. stir in salt to taste. Keep this dal on a low simmer while you make the spicy tomato butter.
heat the ghee or oil in a frying pan over medium-high heat. when hot, add cumin seeds. when they turn dark brown (about 12 seconds), add the onion. fry the onion, stirring constantly, until golden brown (10-12 minutes). add the ginger, garlic, coriander, and chilies, and fry for 2 minutes. (if the seasonings seem to be browning too fast, reduce heat to medium.).
add the tomatoes and continue frying until cooked and the contents of the pan look thick and pulpy. pour the entire mixture over the dal, add garam masala, and mix well. let simmer, covered, for 5 minutes before serving.