(Optional) Heat olive oil in a skillet over medium-high heat. Sear the beef cubes on all sides until browned (about 3-4 minutes).
Place the browned (or raw) beef into the slow cooker.
Add the chopped onions, garlic, carrots, and potatoes to the slow cooker.
In a separate bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Pour this mixture over the beef and vegetables.
Add the bay leaf into the slow cooker.
Cover and set the slow cooker on low for 8 hours or high for 4 hours, until the beef is tender.
Once cooked, remove the bay leaf and taste to adjust seasoning before serving.
For a thicker stew, mix 2 tablespoons of cornstarch with water to create a slurry and stir it in during the last 30 minutes of cooking.