Steam or microwave butternut until fork tender. Puree in a food processor or blender with the water until well mixed. Do not over process or you will end up with soup ;).
Add butter to a small pot and let melt halfway. Add butternut and mix until well incorporated.
Add cinnamon and mix. Taste and add more cinnamon if you want!
Should make approx. 3 cups depending on how big your butternut squash was.