Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Sear half of the beef chuck cubes for about 45 seconds on each side until brown, then transfer to slow cooker. Repeat with remaining cubes.

In the same skillet, sauté the chopped onion for 3-4 minutes until translucent. Add minced garlic and cook for an additional 30 seconds. Transfer to slow cooker.

To the slow cooker, add the diced potatoes, carrots, and celery. Pour in the beef broth and stir in the tomato paste, Worcestershire sauce, salt, and pepper. Place bay leaves on top.

Cover the slow cooker and set to cook on low for 10 hours or on high for 4-5 hours.

For a thicker stew, mix cornstarch with cold water to form a slurry. Stir into slow cooker 10-15 minutes before serving, then cover and cook on high until thickened.