Melt butter in large sauce pan

Add celery, onions, and potatoes and saute over medium heat about 10 minutes

Stir in flour and cook, stirring, about 30 seconds

Gradually add milk and chicken broth and cook, stirring constantly, until soup comes to a boil

Reduce heat, cover and simmer 25 minutes, stirring occasionally

Remove from heat and cool 10-15 minutes

Puree in batches, if necessary, in food processor or in pan with stick blender to desired consistency

Return to saucepan

Add salt, pepper, and cheese

Stir until cheese melts

If thinner soup is desired, add additional milk or chicken broth