Classic Chicken Potpie

Ingredients

• Pastry:
• 3 cups all-purpose flour
• 1 teaspoon salt
• 1/2 teaspoon pepper
• 8 tablespoons unsalted butter, chilled, cut into pieces
• 10 tablespoon solid-stick vegetable shortening, chilled, cut into pieces
• Filling:
• 2 pounds boneless, skinless chicken breast, trimmed of excess fat
• 4 cups low-sodium chicken broth
• 6 tablespoons unsalted butter
• 1 tablespoon vegetable oil
• 1 large red skinned potato, diced
• 1 large onion, chopped
• 3 carrots, cut into 1/2-inch dice
• 2 ribs celery, sliced
• 4 ounces mushrooms, diced
• Salt and pepper
• 1/2 cup all-purpose flour
• 1 1/2 cups whole milk
• 1 cup frozen peas, thawed
• 1 tablespoon fresh thyme
• 1 large egg, beaten