Slow Cooker Beef Stew

Name: Slow Cooker Beef Stew
Ingredients: 1/4 cup all-purpose flour; 2 teaspoons dried thyme; 1 1/2 teaspoons kosher salt, plus more as needed; 1 teaspoon freshly ground black pepper, plus more for serving; 1 teaspoon garlic powder; 1 medium yellow onion; 4 medium carrots; 2 medium stalks celery; 1 pound Yukon gold or red potatoes (about 3 medium); 2 1/4 pounds boneless beef chuck roast or beef stew meat; 2 dried bay leaves; 1 1/2 cups beef broth; 1 tablespoon tomato paste; 1 tablespoon Worcestershire sauce; Chopped fresh parsley leaves, for serving (optional)