Blackberry BBQ Sauce for Crock Pot Pork

INGREDIENTS

1/2 cup

blackberry preserves (seedless)

1 cup

ketchup

1/4 cup

red wine vinegar

1/4 tsp

cayenne pepper

1 tsp

ground mustard powder

1 tbsp

brown sugar (packed)

onion (halved and cut into slices)

2 lb

pork (I prefer pork tenderloin, but a pork butt is also a good option.)

Hamburger rolls (optional)