Crockpot Roast

2 TBS olive oil
1/3 cup brown sugar
1 1/2 TBS apple cider vinegar
1 TBS Worcestershire sauce
1 tsp salt
1 tsp mustard powder
1 small onion, diced
2 cloves garlic, minced
5 lb roast
1/4 cup butter
1 cup katsup

Heat olive oil in skillet: add onions and garlic. Cook until onion is crispy tender. Set onion mixture aside, add roast. Cook over medium-high heat, turning as needed to brown all sides. Set aside
To make onion sauce: combine onion mixture, butter, katsup, brown sugar vinager, and Worcestershire sauce, salt and mustard powder in crock pot, stir well. Turn crockpot to simmer.
Submerge browned roast in onion sauce turning 2 or 3 times. Cover and simmer for 6 to 8 hours or until tender