In a dutch oven over medium heat, fry bacon until crisp. Remove bacon from pot and reserve rendered bacon fat. Meanwhile, season beef generously with salt and and toss with flour to coat.
Working in batches as necessary to prevent over-crowding, fry beef in reserved bacon fat until well-browned on each side, about 5 minutes. Transfer to a plate and repeat with remaining beef.
Once all beef has been browned and removed, add onions and cook until softened and lightly browned, about 5 minutes. Add potatoes, carrots, and celery and cook until softened, about 5 minutes. Stir in garlic until fragrant, about 30 seconds.
Add the Guinness and bring to boil, scraping up the browned bits from the bottom of the pot. Boil for 2 minutes.
To the pot add browned beef, chopped bacon, beef broth, Worcestershire sauce, tomato paste, thyme, and bay leaves. Bring to boil. Reduce heat, cover, and simmer 2 hours or until the beef is tender and the vegetables are cooked through.
Stir in peas. Remove bay leaves and season to taste with salt and pepper. Serve with mashed potatoes.