Melt butter in medium saucepan over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook until fragrant, about 30 seconds.
Add tomato sauce, cider vinegar, rice vinegar, molasses, Worcestershire sauce, brown sugar, mustard, hot sauce, salt, black pepper, and cayenne and stir to combine. Bring to a boil, then reduce heat to low and simmer until slightly thickened, about 15-20 minutes, stirring occasionally.
Transfer sauce to the jar of a blender and blend until smooth. Let cool to room temperature, transfer to a jar and store in refrigerator for up to a month.
2 tbsps unsalted butter
1 onions (small, finely chopped)
2 cloves garlic (minced)
2 cups tomato sauce
1/2 cup cider vinegar
1/3 cup rice vinegar
1/3 cup molasses
3 tbsps worcestershire sauce
2 tbsps dark brown sugar (packed)
2 tsps yellow mustard
1 tsp Louisiana Hot Sauce
1 tsp kosher salt
1 tsp ground black pepper (freshly)
1/4 tsp cayenne pepper