In large saucepan, melt butter. Stir in flour, heat and stir until smooth. Gradually add milk, stirring constantly until thickened.
Add potatoes and onions. Bring to boil, then reduce heat and simmer for 10 minutes. Add remaining ingredients; stir until cheese is melted. Serve immediately.
Variation: Nueske Smoked Bacon may be substituted for ham (6 slices, diced, fried and drained).