In large ziploc bag add your flour, salt, pepper and stew meat and shake to coat.
In large skillet add your oil and heat over medium high heat.
Add your stew meat and brown on all sides to lock in flavor, set aside.
In large 6-8 quart crockpot add your potatoes, carrots, celery, onion, garlic and tomato paste.
Add in stew meat, beef broth, Worcestershire sauce, Guinness and bay leaves and stir to coat.
Heat on low for 6-8 hours,
30 minutes before serving stir together cornstarch and water and mix into beef stew and stir around, cook on high for 30 minutes or until desired thickness is reached.
Remove bay leaves before serving.