Carolina Style Barbecue Sauce

• 1 cup prepared yellow mustard
• 1/2 cup sugar
• 1/4 cup light brown sugar
• 3/4 cup cider vinegar
• 1/4 cup water
• 2 tablespoons chili powder
• 1 teaspoon black pepper
• 1 teaspoon white pepper
• 1/4 teaspoon cayenne
• 1/2 teaspoon soy sauce
• 2 tablespoons butter
• 1 tablespoon liquid smoke (hickory flavoring)