Season beef pieces:
Pat the beef pieces dry with paper towels. Season with salt and pepper; set aside.Sauté vegetables:
In a Dutch oven or heavy-bottomed soup pot, heat 2 tablespoons olive oil over medium-high heat. Add carrots, onion, celery, and mushrooms; sauté until softened and just beginning to brown. Remove vegetables from pot and set aside.Sear beef batches:
Add remaining 2 tablespoons olive oil to the pot. Sear beef in batches until browned on all sides. Return all beef to the pot.Make flour roux:
Add butter and flour to the beef; stir to coat. Cook for 2-3 minutes, stirring frequently to prevent burning.Deglaze with beer:
Deglaze the pot with Guinness beer, scraping up any browned bits from the bottom.Add seasonings:
Add rosemary, thyme, bay leaves, tomato paste, chicken bouillon, garlic powder, 2 teaspoons brown sugar, 1 teaspoon black pepper, and 1/4 teaspoon salt. Stir to combine.Pour broth mixture:
Add beef broth and water; mix well. Return cooked vegetables to the pot.Simmer for hours:
Bring to a boil, then reduce heat to a simmer. Cover and let simmer for at least 2 hours, stirring occasionally.Adjust seasoning:
About halfway through, taste and adjust seasoning with additional salt, pepper, or brown sugar as needed.Serve over potatoes:
Once beef is tender, serve over mashed potatoes.