Heat 2 tablespoons olive oil in a large heavy pot over medium-high heat until shimmering.

Season the beef cubes with salt and pepper. Work in batches to avoid overcrowding; brown each batch on all sides (about 3–4 minutes per batch). Transfer browned beef to a plate.

In the same pot, add the diced onion and sliced carrots. Cook until the onion softens and the vegetables begin to color, about 5–7 minutes. Add the minced garlic and cook for 30–60 seconds until fragrant.

Return the beef to the pot. Stir in 2 tablespoons of tomato paste and cook for a minute to deepen the flavor.

Pour in 2 cups of Guinness beer to deglaze the pan, scraping up the fond. Add 4 cups of beef broth, 1 teaspoon of dried thyme, 1 teaspoon of dried rosemary, and season with salt and pepper.

Bring the liquid to a gentle boil, then reduce heat to low so the stew simmers gently. Partially cover and simmer for about 2 hours, or until the beef is fork-tender. Stir occasionally and skim any excess fat if desired.

For a thicker stew, mix 2 tablespoons of cornstarch with 2–3 tablespoons of cold water to make a slurry. Stir the slurry into the stew during the last 10 minutes of cooking and simmer until the sauce thickens. Taste and adjust seasoning.

Serve hot, sprinkled with chopped parsley.