Cook onion and garlic in a couple tablespoons of butter until soft, not brown. Set aside. Make a roux by melting the butter and whisking the 1/2 cup of flour in. Boil for 3 minutes stirring constantly. Add the onion and garlic to the roux.
Add the half and half and chicken broth. Simmer 3 minutes or until thick.
Pour mixture into a crockpot then add the white beans, chilies, chicken, cheese, Tabasco sauce, chili powder, and cumin.
Cook 60 minutes in the slow cooker (or longer if needed). Right before serving add salt and pepper to taste and sour cream (optional). Garnish with cilantro.