Melt butter in large saucepan over medium heat. Add onion; cook and stir until tender. Add flour, salt and pepper; cook, stirring constantly for 1 minute.
Add milk. Increase heat to medium-high and bring to a boil, stirring constantly. Boil and stir 1 minute. Add corn and sausage; return to a boil.
Reduce heat to medium-low and simmer 10 minutes. Stir in potatoes; heat through.
Top each serving with parsley and cheese, if desired.
