Place meat, stock, balsamic vinegar, salt, pepper, rosemary, bay leaves, onion and garlic into a crockpot and stir. Cover and cook on low 6 to 8 hours or on high 4-6 hours. {You just want to cook it until the meat basically just melts in your mouth...3 steps beyond fork tender.}

Using a slotted spoon, remove the meat to a separate bowl and discard the rosemary sprig stalks and the bay leaves.

In a separate, microwave-safe bowl, place flour and slowly mix in about 3/4 of the cooking liquid from the crockpot until smooth. Microwave 1 minute or until mixture thickens {will look super thick and gross....this is normal!}

Whisk this paste into the remaining liquid to create a gravy. Taste, adjust seasonings and add in another 2-3 tablespoons of balsamic vinegar of desired.

Return meat back to the crockpot and stir to coat. Serve over mashed potatoes or rice...or just by itself!