Trim all visible fat from beef roast. Season with salt and pepper.
Spray a large skillet over high heat with a light oil spray (I used grapeseed oil spray). Sear all sides of the roast until dark brown.
Add onion, garlic, stock, soy sauce, Worcestershire sauce, rosemary, and bay leaves to your slow cooker or instant pot. Place beef on top and cover with lid.
For the slow cooker, cook on high heat for 4-5 hours or low heat for 7-8 hours. You'll know it's done when the meat pulls apart easily. Remove beef, shred, and return to jus. Cover and let rest on warm setting for 30 minutes, or on low if you don't have a warm setting.
For the instant pot, cook for 45 minutes on high pressure, then quick release. Remove beef, shred, and return to jus. Cover and let rest on warm setting for 30 minutes.