Wash and sort the beans the night before. Place them in a pot and cover them with 2 inches of water. Let them soak overnight (or all day if you are preparing for dinner).
Pour the soaking water off the beans and then add water to cover by at least 1 1/2 inches. Bring to a boil and cook for 30 minutes. Remove from heat and set aside.
While the beans are cooking, trim the leaks and wash with cold water, being careful to wash away the dirt deep in the tops. Slice the leeks in half lengthwise and chop into 1 inch pieces.
In a large stockpot melt the 6 tbsp butter and cook the leeks on medium-low heat until tender.
Sprinkle the flour over the leeks. Cook for 2 minutes. Increase the heat to high and stir in the chicken stock.
Add the potatoes, sliced sausage, cooked white beans, and creole seasoning. Bring to a boil. Reduce the heat to medium low and simmer until the potatoes and beans are tender. Use a paper towel to absorb any grease from the sausages that has accumulated on the top of the stockpot. Season with salt and pepper to taste. (Taste first -- the sausage will add some salt to the soup) If desired, add the remaining stick of butter before serving. (I usually skip this).