Pat the beef stew meat dry with paper towels. In a shallow dish or large bowl, combine the all-purpose flour, 1 teaspoon salt, and 1/2 teaspoon black pepper. Dredge the beef cubes in the flour mixture, shaking off any excess. Set aside.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Sear the beef in batches until browned on all sides, about 2-3 minutes per batch. Do not overcrowd the skillet. Transfer the seared beef to the slow cooker insert.

Add the remaining 1 tablespoon of olive oil to the same skillet (or add a little more if needed). Add the chopped yellow onion and cook until softened, about 3-5 minutes. Add the minced garlic and cook for another minute until fragrant.

Stir in the tomato paste and cook for 1 minute, stirring constantly, to deepen its flavor. Pour in the beef broth, scraping up any browned bits from the bottom of the skillet. Stir in the Worcestershire sauce and dried thyme. Bring to a simmer.

Pour the broth mixture over the beef in the slow cooker. Add the bay leaf. Cover and cook on low for 6-7 hours, or on high for 3-4 hours, until the beef is tender.

After the initial cooking time (when beef is tender), add the peeled and chunked Yukon Gold potatoes, sliced carrots, and sliced celery to the slow cooker. Stir gently to combine. Cover and continue to cook on low for an additional 1.5-2 hours, or on high for 45-60 minutes, or until the vegetables are tender.

If using, stir in the frozen peas during the last 15 minutes of cooking. Remove the bay leaf before serving.

Taste and adjust seasoning if necessary. Ladle the hearty beef stew into bowls, garnish with fresh chopped parsley if desired, and serve warm with crusty bread.