Melt butter in a large sauce pan, over medium heat. Add the onions, celery, and green pepper. Sauté over medium heat for about 10 minutes, until vegetables begin to soften. Add garlic; cook until fragrant, about 30 seconds. Add salt, sugar, cayenne pepper, and flour; stir to combine. Add diced tomatoes, chicken broth, Worcestershire sauce, and hot sauce. Bring the mixture to a boil; cover pan and reduce heat to low. Simmer for 30 minutes, or until vegetables are tender.