Combine 1/2 of the water and a handful of the spinach in a jar of a blender. Blend at high speed for 30 seconds. Keep adding spinach until about half is blended. Add a little more water, if necessary, to puree.
In a large skillet, heat the butter over moderate heat. Add the ginger and saute for one minute. Add the onions and salt and continue sauteing for 5 more minutes.
Stirring after each addition, add the cumin, turmeric, coriander, and garam masala. Then stir in the leafy and pureed spinach. Reduce the heat and cook the mixture uncovered, for 20 to 30 minutes. Most of the liquid should evaporate. At the last minute, gently add the paneer. Serve hot.