Melt butter in large saucepan over medium heat. Add onion; cook, stirring occasionally, for 1 to 2 minutes or until tender. Stir in flour. Gradually stir in broth and evaporated milk.

Scoop potato pulp from one potato; mash. Add pulp to broth mixture. Cook over medium heat, stirring occasionally, until mixture just comes to a boil.

Dice remaining potato skin and potato(es); add to soup. Heat through. Season with salt and pepper. Top each serving with bacon, cheese and green onion.