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

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

Dice remaining potatoes, with skin. Add the sausage and potatoes to soup. Heat through. Season with salt and pepper. Top off each individual bowl with sliced green onion and cheese.