Melt butter over medium-low heat in a medium saucepan. Add onions and cook for around 5 minutes, stirring constantly. You want your onions soft, but not browned.
Add mustard powder and flour, stirring as you go, so there are no lumps. Cook for one minute.
Pour in 2 cups of milk, stirring as you go, again NO LUMPS!
Pour in 1 cup chicken broth and season with cayenne, Worcestershire, salt and pepper.
Add corn; stir. Let simmer for 5 minutes.
Add cheese and stir until melted. Simmer for another 5 minutes.
Adjust seasonings accordingly and serve with bacon or croutons and parsley.