Clean, wash and roughly chop the spinach.
Heat a pan and saute spinach for few minutes till it gets soft.
Let it cool down a bit and then puree it in the blender or food processor.
In the same pan heat oil, saute garlic and then oregano and mixed herbs.
Add pureed spinach and milk. Cook on high flame for few minutes till the desired consistency is reached.
Add mayonnaise, though optional.
Lastly, add salt. Give one last boil and switch off the flame. Spinach sauce is ready.