Grind the onions, tomatoes and garlic to a smooth paste and keep it aside. Now whip the roughly chopped spinach in the blender and keep it aside. Heat oil in a heavy bottom pan and fry the cumin seeds until they turn dark.
Add the onion-tomato mixture. Cover and cook until the gravy becomes thick.
Tip in the spice powders and salt. Stir until well blended.
Now, add the spinach puree.
Reduce the heat and cook for about 10 mins.
Switch off the flame. Finally add yogurt and mix well until well-blended.