Put the oil in a large, wide pot and set over medium-high heat. When very hot, put in the chile, onions and garlic. Stir and fry until the onions turn medium brown. Add the tomato. Stir and fry for 2 minutes. Now put in the spinach and salt. Cover, allowing the spinach to wilt. Stir, turn the heat to medium, cover again, and cook for 25 minutes. Uncover, add the garam masala, and stir. Cook, uncovered, another 5 to 6 minutes, or until almost no liquid is left is left at the bottom of the pan. Turn up the heat during this period, if needed.
Recipe courtesy of Madhur Jaffrey, World Vegetarian, Clarkson Potter, 1999