Beef and Barley Stew

Name: Beef and Barley Stew
Ingredients: 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, plus more; 1 tsp. freshly ground pepper, plus more; 1½ lb. beef stew meat (such as boneless chuck), cut into ¼ cubes; 1 Tbsp. vegetable oil; 1 large red onion, finely chopped, plus more thinly sliced for serving; 3 medium carrots, peeled, cut into ¼-thick rounds; 2 medium celery stalks, finely chopped; 8 garlic cloves, finely grated; ¼ cup double-concentrated tomato paste; 4 cups low-sodium beef broth; 1 cup pearl barley; 2 Tbsp. Worcestershire sauce; Parsley leaves with tender stems (for serving)