Heat 1 tea spn butter. When it melts, add spinach and fry for 1-2mins. Add 1 cup water and cook till spinach leaves become tender. Grind them into a smooth puree using mixer/blender.
heat remaining butter and fry onions till they turn translucent. Now add spinach puree. Mix corn flour in milk or water and add this to the spinach mixture stirring continuously. Add salt and pepper. When it thickens to desired consistency, take off from heat.