Chop up leeks and mushrooms, put into large pot, add butter and saute until soft (about 30 minutes). Once soft, stir in flour, salt, white pepper and cook for an additional 10 minutes (stir often). Add all chicken broth and bring to a boil. Turn down heat and simmer for about 30 minutes. Remove from heat and let cool (not too cool). Use a blender and puree a little at a time. Once pureed to desired consistency, pour back into a pot or a crock pot, add half and half and reheat. Heat till warm/hot, but do not boil. DONE!