Pat the beef cubes dry and season generously with salt and pepper. Toss with flour until lightly coated; shake off excess.

Heat oil in a heavy Dutch oven over medium-high heat. Brown beef in batches until deep mahogany on all sides (do not crowd the pan). Transfer browned meat to a plate.

Reduce heat to medium, add a bit more oil if needed, and sauté the onion until soft and lightly caramelized, about 6–8 minutes. Stir in garlic for 30 seconds.

Add tomato paste and cook for 1 minute to remove raw flavor.

Pour in Guinness to deglaze, scraping up browned bits from the bottom. Let the beer reduce by a third (1–2 minutes).

Return the beef to the pot. Add beef stock to cover most of the beef (leave some exposed for evaporation), plus bay leaves and thyme.

Bring to a simmer, then reduce heat to low, cover, and cook gently until the beef is very tender: 2–3 hours on the stove, or 6–8 hours on LOW in a slow cooker.

About 45–60 minutes before the end, add carrots and potatoes so they become tender but not mushy.

If the broth is thin at the end, thicken with a cornstarch slurry (1 tbsp cornstarch mixed with 1 tbsp cold water) or a beurre manié (equal parts softened butter and flour). Stir in small amounts until you reach your desired consistency.

Remove bay leaves and thyme stems, adjust salt and pepper, and finish with chopped parsley.