Melt butter in a pot at medium heat. Add chopped onion and cook until soft. Add flour and cook for a minute.
Add chicken broth and cook until boiling, stirring frequently. Add creamed corn and cook until boiling again.
Pour the thick soup into a blender, and mix until very smooth. Strain through a sieve, and pour back into a pan. Add milk and cook until hot. Add salt and pepper to taste. Garnish with parsley to serve.