Season beef with 1 teaspoon salt and 1/2 teaspoon pepper.
Heat olive oil in a large stockpot or Dutch oven over medium high heat. Working in batches, add beef to the stockpot and cook, stirring occasionally, until evenly browned, about 6-8 minutes; set aside.
Reduce heat to medium. Add onion, carrots and celery. Cook, stirring occasionally, until tender, about 3-4 minutes.
Stir in garlic until fragrant, about 1 minute.
Whisk in flour and tomato paste until lightly browned, about 1 minute.
Stir in Guinness, scraping any browned bits from the bottom of the stockpot.
Stir in beef stock, Worcestershire, thyme, bay leaves and beef. Bring to a boil; reduce heat and simmer, partially covered, until beef is very tender, about 2 hours, stirring occasionally.
Remove and discard thyme sprigs and bay leaves. Stir in parsley; season with salt and pepper, to taste.*
*TO FREEZE: Let cool completely; portion into plastic freezer bags in individual servings, squeezing out any excess air before sealing. Lay the bags flat in a single layer in the freezer (this will help them freeze quickly). To reheat, thaw overnight in the fridge, reheating over low heat, stirring occasionally, until heated through.