Pat the beef cubes completely dry with paper towels. In a shallow dish or a large zip-top bag, whisk together the flour, salt, pepper, and paprika. Add the beef cubes and toss until they are evenly coated.

Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Working in two batches, add the beef in a single layer and sear until deeply browned on all sides, about 5-7 minutes per batch. Do not overcrowd the pan. Transfer the browned beef to the insert of your slow cooker.

Reduce the skillet heat to medium. Add the chopped onion to the same skillet and cook, stirring occasionally, until softened, about 5 minutes. Add the minced garlic and tomato paste, and cook for another minute until fragrant, stirring constantly.

Pour about 1/2 cup of the beef broth into the skillet. Scrape the bottom of the pan with a wooden spoon to release all the flavorful browned bits (this is called deglazing). Pour the entire mixture from the skillet into the slow cooker over the beef.

To the slow cooker, add the remaining beef broth, Worcestershire sauce, balsamic vinegar, dried thyme, and the bay leaf. Add the prepared potatoes, carrots, and celery. Stir everything gently to combine.

Cover the slow cooker and cook on LOW for 7-8 hours or on HIGH for 4-5 hours, until the beef is fork-tender and the vegetables are soft.

Once cooked, remove and discard the bay leaf. Stir in the frozen peas; they will cook through from the residual heat in about 5 minutes. Taste the stew and adjust seasoning with additional salt and pepper if needed.

If you prefer a thicker gravy, you can make a slurry by whisking 2 tablespoons of cornstarch with 3 tablespoons of cold water in a small bowl until smooth. Stir the slurry into the stew, turn the slow cooker to HIGH, cover, and cook for 15-20 minutes until the gravy has thickened.

Ladle the hot stew into bowls, garnish with fresh parsley, and serve immediately with crusty bread for dipping.