Coat each side of the roast with oil. Combine the salt, pepper, onion powder, garlic powder, and dried rosemary in a dish. Sprinkle evenly all over both sides of the roast.
3-4 lb chuck roast, 1.5 tablespoon olive or avocado oil, 1 teaspoon kosher salt, ½ teaspoon pepper, ½ teaspoon onion powder, 1 teaspoon garlic powder, 1.5 teaspoon dried rosemary
Heat a large skillet over high heat (I like to use cast iron, but any skillet will work well). Once the skillet is hot, sear each side of the roast for 2-3 minutes, allowing a golden brown crust to form. Place roast in slow cooker.
Pour the beef broth in the hot skillet, then add the balsamic vinegar, mustard, and brown sugar. Whisk well and simmer for 1 minute, scraping up the brown pieces from the bottom of the pan as you stir. Pour the mixture over the meat in the slow cooker.
1 cup beef broth, ¼ cup balsamic vinegar, 1 tablespoon dijon mustard, 1 tablespoon brown sugar
Cook on low for 8-10 hours or high for 4-4.5 hours, or until it falls apart easily when prodded with tongs or forks.Around hour 7 (or 3.5-4 if your slow cooker is on high) begin checking for tenderness with a fork. Once the roast just begins to fall apart around the edges, dissolve the cornstarch in the water and pour into the liquid left in the slow cooker. Stir well to combine. Cover and allow to cook one more hour (or about 30 minute if it's on high). ⅓ cup water, 1 tablespoon cornstarch
After an hour, the gravy should be thick enough to coat the back of a spoon. If it isn't, leave the slow cooker on high with the lid off while you prepare the meat in the next step. That will allow extra water to evaporate, thickening the juices.
Use tongs to move the meat onto a cutting board. Use two forks to gently remove any large chunks of fat and discard it. Then use the forks to pull the meat apart into bite sized chunks.
You can strain the remaining cooking liquids to remove chunky bits if needed, but it is optional. Stir the meat and liquids back together in the slow cooker, then serve with your favorite sides (mashed potatoes and veggies are our favorite!).