Put all ingredients in crockpot except for butter and flour. Cover and cook on Low for 8 to 10 hours. One hour before serving, turn on High. Make a roux of 1 stick butter and 1/2 c. flour (melt butter in small saucepan, on med-low heat, and stir in flour); stir until smooth. Pour into crockpot and stir into soup. Cook soup on High until thickened.