Thats Roxy's finishing sauce... I just made up a batch...Mustard Vinegar Sauce:
1 cup apple cider vinegar
1/2 cup yellow mustard
1/4 cup onion finely minced
2 cloves garlic pureed
1/2 teaspoon black pepper
1 tablespoon Worcestershire sauce
1/2 cup brown sugar
1/4 teaspoon cayenne pepper
1/2 teaspoon salt
1/2 teaspoon Tabasco sauce
Blend on high then simmer for 15 minutes stirring occasionally
Got an 8lb butt on and I made some Boursin cheese au gratin potatoes...
Ill post pics in a bit, just about to get it out of the cooler to pull it.