chicken and sausage gumbo

I found this recipe in my Food Network Magazine.  This recipe has won a first-place trophy in a gumbo cooking competition.  I have always liked gumbo and this was a fantastic recipe.   It makes enough for two families.

chicken and sausage gumbo (Food Network Magazine, October 2012)
2/3 cup canola oil
3/4 cup white flour
1/4 cup whole wheat flour
1/4 cup finely chopped onion plus 2 cups roughly chopped
1 cup low-sodium chicken broth
1 cup chopped celery
1/2 cup chopped green bell pepper
2 teaspoons cayenne pepper(1 teaspoon was plenty!!)
1 teaspoon garlic powder
kosher salt and freshly ground black pepper
1 pound smoked sausage, sliced (I used smoked turkey sausage)
8 ounces tasso ham or andouille sausage, diced
1 1/4 pounds skinless, boneless chicken thighs, cut into 1-inch pieces
1 1/4 pounds skinless, boneless chicken breasts, cut into 1-inch pieces
3 to 4 scallions, chopped
cooked white rice for serving

Make the roux:  Heat the canola oil in a cast-iron skillet over medium heat until hot, about 5 minutes.  Whisk in both lours and cook, whisking constantly, until the roux is dark brown, about 10 minutes.  Remove from the heat and let stand 10 minutes, then stir in the finely chopped onion.
Meanwhile, bring the broth and 20 cups water (yes, 20) to a boil in a large pot.  Add the roughly chopped onion, the celery and bell pepper; cook over medium-high heat, 15 minutes.  Stir in the roux in 3 batches; cook, stirring occasionally until thickened, 30 minutes.  Add the cayenne, garlic powder, 2 1/2 tablespoons salt and 1/2 teaspoon black pepper.  Stir in the smoked sausage and tasso.  Reduce the heat to low; simmer 1 hour.  
Return the mixture to a boil.  Add the chicken thighs and breasts and cook 30 minutes.  Remove from the heat.  Skim the fat off the surface, then stir in the scallions.  Serve over rice.