This recipe has been a family favorite for 35 years. Serve on hamburger buns that have been buttered on both halves, and lightly browned under broiler. Freeze some for lunches or dinner in a hurry.
Place roast in a large covered pan. Roast at 325 degrees F (165 degrees C) for 2 hours, or until the meat falls apart and shreds easily.
In a large skillet, melt butter over medium heat. Add onions, and saute until onions become translucent.
Stir in vinegar and chili sauce. Fill empty chili sauce bottle with water, shake, and pour liquid into skillet. Mix in brown sugar, mustard, Worcestershire sauce, black pepper, salt, cayenne pepper, and garlic. Cook sauce over low heat, stirring often, until thickened.
With two forks, shred roasted beef. Stir meat into the sauce in the skillet, and simmer for 30 minutes.
