Spray the inside of the slow cooker with cooking spray.
Heat the butter and olive oil in a cast-iron pan over medium-high heat. Add the onion and celery and sauté for 3 to 4 minutes, or until translucent. Add the garlic and sauté for another minute. Transfer the onion, celery, and garlic to the slow cooker and add the tomatoes, tomato sauce, thyme, sugar, Worcestershire sauce, chili powder, salt, cayenne, and bay leaves. Cover and cook on low for at least 6 hours and up to 8 hours.
One hour before serving, add the bell pepper and continue to cook on low. Finally, during the last 10 minutes, add the shrimp and cook until they are pink and slightly curled (be careful not to overcook). Season with salt and pepper. Remove the bay leaf and spoon over rice. Garnish with a sprinkling of fresh chives. Serve with hot sauce on the side.
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