Chicken Pot Shepherds Pie

Name: Chicken Pot Shepherd’s Pie
Ingredients: 3 lb. russet potatoes, peeled and cut into 1-inch pieces; Kosher salt and freshly ground black pepper; 4 1⁄2 cups milk; 14 tbsp. unsalted butter; 2 lb. chicken breast, cut into 1-inch pieces; 10 oz. button mushrooms, quartered; 1⁄2 medium yellow onion, finely chopped; 1 red bell pepper, stemmed, seeded, and finely chopped; 1⁄2 cup flour; 1 cup fresh or frozen peas; 2 sheets puff pastry; 1 egg, lightly beaten