In a heavy pot, heat the ghee or oil until shimmering. Add onion and cook slowly, stirring often, until golden, about 20 minutes. Add ginger, garlic, tomato paste, garam masala and chili powder. It should be thick, but not pasty; it should drip off a spoon. If too thick, add more ghee or oil. Cook until very fragrant, 3-4 minutes.