In a large heavy skillet over medium-high heat, add the oil, swirling to coat the bottom of skillet. Once hot, place the roast in skillet and cook for 3-4 minutes on each side to sear it.

Place the sliced onions in the bottom of the slow cooker. Place the roast on top of the onions in the slow cooker. Sprinkle the salt, pepper, thyme, and minced garlic over top of the roast, rubbing it into the top and sides.

Add the potatoes and carrots around the outside of the roast. Pour the broth over the vegetables.

Place the lid on the slow cooker and cook for 8-10 hours on low, or for 6-7 hours on high.

Remove the meat to a large platter, rimmed sheet pan, or cutting board. Use two forks to shred or pull the meat apart into pieces. Serve the shredded meat with the cooked onions, potatoes, and carrots.

To make the optional gravy: Transfer about 1 ½ cups of the liquid from the slow cooker to a small saucepan over medium-high heat.

In a small dish, stir together 3 tablespoons of water with 2 tablespoons of cornstarch until a smooth milky liquid forms (this is called a slurry).

Slowly stir the slurry into the liquid in the saucepan. Bring to a boil, then reduce the heat to maintain a simmer. Whisk continuously until thickened, 2-3 minutes.

Remove the gravy from the heat and season with salt and pepper to taste. Serve gravy over the beef and vegetables.