In a small bowl, whisk together the tomato sauce, beef broth, minced garlic, thyme, Worcestershire sauce, and white wine vinegar.

Prepare the chuck roast by trimming any excess fat. Season all sides of the meat generously with salt and black pepper.

Place half of the thinly sliced onions in the bottom of your slow cooker.

Pour half of the prepared sauce over the onions.

Place the seasoned chuck roast on top of the onions, then sprinkle the remaining onions over the meat.

Pour the rest of the sauce over the top.

Cover and cook on high for 4 hours or on low for 7 hours until the meat is fork tender.

Once done, remove the roast and onions from the pot.

To make the gravy, measure the sauce from the slow cooker. For every 1 cup of sauce, use 1 tablespoon of flour or cornstarch.

Heat the sauce in a small saucepan over low heat, whisking in the thickener until the gravy reaches your desired consistency.

Serve the pot roast with plenty of gravy, ideally over mashed potatoes, and garnish with fresh parsley.