In a large plastic bag, add the flour along with the salt, pepper, oregano, thyme, and onion powder.
Add the beef to the bag and shake until the beef is completely coated.
Heat a large skillet to medium high. When hot, add the oil.
Add the flour coated beef. Brown the meat on all sides, being careful not to let it burn.
When the meat is browned, add the tomato paste and beef broth.
Stir the beef, tomato sauce, and beef broth until a thick gravy forms. Be sure to scrape up any flavorful browned bits stuck to the bottom of the pan! Remove from heat and set aside.
Add the potatoes, carrots, celery, onion, and garlic to the slow cooker.
Pour the beef and sauce mixture over the veggies.
Stir in the Guinness beer and place bay leaves on top.
Cover and cook on LOW for 8 hours. Try to avoid opening the lid while cooking!
Remove bay leaves. Serve.