First of all heat butter in a deep non stick pan, now add onions and garlic, saute it on a medium flame till the onions become translucent.
Now add spinach and saute on a medium flame for 2 minutes then add 2 cups water, mix well and cook on medium flame for 7-8 minutes stirring occasionally, now allow it to cool completely.
When it gets completely cooled, blend it in a mixture blender to make a smooth puree then strain the puree with a sieve and transfer it to a pan.
Now combine the corn flour water mixture and cream in a bowl and mix well, make sure that there is no lumps then add it to the spinach puree and mix well.
Now cook it on a medium flame for 1 minute stirring occasionally, then take out in a serving bowl, garnish it with butter and enjoy.