Gumbo Burgers with Roux “Ketchup”

• 2 tablespoons salted butter
• 1 cup chopped onion (from 1 [4 1/2-oz.] onion)
• 1/2 cup chopped celery (from 2 stalks)
• 1/2 cup chopped green bell pepper (from 1 [6-oz.] pepper)
• 12 ounces medium-size peeled, deveined raw shrimp
• 3 ounces chopped andouille sausage
• 1 1/2 cups cooked white rice
• 1/2 cup chopped scallions (from 2 scallions)
• 1 1/2 teaspoons creole seasoning
• 1 1/2 teaspoons filé powder
• 2 tablespoons canola oil

ADDITIONAL INGREDIENTS

• 4 onion rolls, split and toasted
• 8 pickled okra spears, split lengthwise