Chicken Pan Pie

Name: Chicken Pan Pie
Prep time: 20 min
Cook time: 1 h
Total time: 1 h 20 min
Cuisine: American
Ingredients: 0.25 cup unsalted butter; 0.66666668653488 cup diced onion; 0.5 teaspoon kosher salt, or to taste; 1.5 pounds boneless, skinless chicken thighs, cut into 1-inch pieces; 0.25 cup all-purpose flour; 2.5 cups chicken broth; 0.5 cup sliced carrots; 0.5 cup sliced celery; 0.25 teaspoon freshly ground black pepper; 1 pinch cayenne pepper; 0.5 cup frozen peas, thawed; 1 teaspoon fresh thyme leaves; 1 recipe pastry pie dough; 1 large egg, beaten; 2 teaspoons water