In a 4qt Dutch oven melt butter, add onions and celery. Saute over medium heat until onions turn golden.
Add chicken broth and potatoes to sauted vegetables. Bring to a boil, reduce heat and simmer covered for 10 minutes, or until potatoes are cooked. With a potato masher mash ingredients several times until they are coarse but still chunky. Turn off heat.
In a small bowl, combine flour, milk, half and half and buttermilk. Blend until smooth. Add to the soup all at once stirring constantly until thoroughly mixed. Turn the heat on and heat for about 10 minutes on low to let the flour dissolve and disburse to thicken the soup.
Serve soup topped with cheddar cheese, bacon bits, chopeed green onions and sour cream. It makes a hearty little meal. Note: I have given this recipe to several people and a few have told me that they have a hard time heating the soup back up as described in "step 3" above. They say that the soup tends to stick to the bottom of the pot. If this happens, you can always mix the flour, milk, half and half and buttermilk in a separate small pot and heat it until it thickens and then pour it into the potato soup stirring constantly until it is blended. I hope you enjoy my recipe for potato soup.