Add the celery, onion, and carrots to the bottom of your slow cooker.
Mix together the rosemary (crush it slightly as you add it to a small bowl), thyme, salt, pepper, and garlic powder. Generously season the roast with the spice mixture.
Heat a 12 inch cast iron skillet over high heat and add about 2 tablespoons of canola or coconut-canola oil. When the oil is hot, sear the roast for 2-3 minutes a side until a nice crust develops. Don’t forget to sear the edges. Place the roast in the slow cooker.
Add the beef broth, worchestershire, and water to the hot skillet. Scrape the bottom of the pan with a flat whisk. Bring the mixture to a boil and reduce by half. Pour over the roast in the slow cooker.
Cook on low for 8 hours.
Remove roast from slow cooker and cover with foil for about 5-10 minutes before slicing. Use this time to make gravy if desired. Slice or shred into large chunks.
Serve with mashed potatoes.