In a pot on medium heat, melt butter and oil together. Add in potato and cook for 7-8 minutes, frequently stirring. Once potatoes are soft, add in corn and sugar and stir fry another 1-2 minutes.
Add in water, milk and salt. Mix lightly then remove from heat. Allow to cool for 8-10 minutes, then pour into a blender or food processor. Blend until smooth.
Pour soup back into pot and turn to medium heat (optional: strain soup through a sieve). Add in cream cheese, heavy cream and fish sauce. Bring to a simmer and cook over medium-low heat another 2-3 minutes, occasionally stirring.
Top with a sprinkle of parsley and enjoy!
