Preheat oven to 375°F (190°C). On a rimmed sheet pan, toss carrots and celery with 1 teaspoon olive oil, salt and pepper. Roast until lightly caramelized, about 20 minutes.

Meanwhile, season beef with 1 teaspoon salt and ½ teaspoon pepper. Heat remaining olive oil in a Dutch oven over medium-high. Working in batches, sear beef on all sides until deep brown, 6–8 minutes per batch. Transfer meat to a plate.

Reduce heat to medium. Add onion and cook until translucent, 3–4 minutes. Stir in garlic and cook until fragrant, about 1 minute.

Sprinkle in flour and tomato paste; cook, stirring constantly, until edges darken, about 1 minute.

Pour in Guinness, scraping browned bits from bottom. Add beef stock, Worcestershire, thyme, bay leaves and all seared beef. Stir to combine.

Nestle roasted carrots and celery into stew. Bring to a gentle simmer. Cover and transfer pot to oven; braise for 2 hours, stirring once halfway through.

Remove thyme sprigs and bay leaves. Stir in parsley, adjust seasoning with salt and pepper. Let rest 10 minutes before serving.