Trim excess fat from the beef chuck roast and season it with salt and pepper. Sear the roast in a large skillet over medium-high heat for about 4-5 minutes per side until brown.

In the slow cooker, place the seared beef chuck roast. Add chopped onions and minced garlic on top. Pour in the beef broth, ensuring everything is well-coated. If desired, add the optional gravy mix.

Cover and set the slow cooker to low for 8 hours or high for 4-5 hours until the beef is fork-tender.

Peel and chop the high-starch potatoes into even chunks. Boil in salted water for about 15-20 minutes until tender. Drain and mash with butter, cream, and salt.

Shred the beef in the slow cooker, mixing it with the gravy. Serve with mashed potatoes and garlic bread on the side.