Preparation / Directions:
In a sauce pan, combine tomato sauce, mustard and vinegar and bring to a simmer over medium heat. Do not boil.
In a blender, puree the onions and bell peppers in the water. Transfer to a small saucepan, bring to a simmer and cook over medium-high heat for 2 to 3 minutes. Add to the tomato sauce mixture and stir well to blend. Continue to simmer the mixture.
In a bowl, combine the brown sugar, salt, pepper, celery powder, onion powder, garlic powder, and paprika. Mix thoroughly. Add a quarter of the dry ingredients to the sauce in the pan. Stir and simmer for 15 minutes. Add another quarter of the dry ingredients, stir and simmer for another 15 minutes. Continue in this manner until all dry ingredients are added. Do not boil sauce.
Cover and reduce heat to low. Cook the sauce for 30 minutes more until it thickens. Transfer to a glass jar and refrigerate for 24 hours before using.