Trim the stewing beef of any excess fat or gristle.
Cut the beef into 2-inch cubes.
Place the beef in a large bowl.
Add 1 tablespoon of vegetable oil and toss until the beef is lightly coated.
In a small bowl, combine the flour, salt, freshly ground black pepper, and cayenne pepper.
Sprinkle the flour mixture over the beef.
Toss until the beef pieces are evenly coated.
Heat the remaining 2 tablespoons of vegetable oil in a large skillet over high heat.
Add the beef to the skillet.
Brown the beef on all sides, working in batches if necessary to avoid overcrowding.
Reduce the heat.
Add the chopped onion, crushed garlic, and tomato paste dissolved in water to the skillet.
Cover and cook gently for 5 minutes.
Transfer the beef mixture from the skillet to a large pot.
Pour 1 bottle of Guinness into the skillet.
Bring the Guinness to a boil.
Stir and scrape the bottom of the skillet to loosen the caramelized meat juices.
Pour the Guinness mixture over the beef in the large pot.
Add the second bottle of Guinness to the pot.
Add the baby carrots, sliced mushrooms, potato chunks, bay leaves, and fresh thyme.
Stir until the ingredients are evenly combined.
Taste and adjust the seasoning if needed.
Cover the pot.
Simmer over low heat for 2 to 3 hours, or until the beef is tender.
Stir occasionally during cooking.
Remove the bay leaves and thyme stem before serving.
Garnish with chopped parsley.
Serve hot.