The Ultimate Chicken Potpie

Ingredients

• 2 tablespoons butter
• 1 large onion, chopped
• 3 medium carrots, peeled and chopped
• 3 stalks celery, chopped
• 1 pint cremini mushrooms, chopped
• 3 garlic cloves, minced
• 1 tablespoon fresh thyme
• 1 tablespoon fresh rosemary
• Salt and freshly ground black pepper
• ⅓ cup all-purpose flour
• 4 cups chicken broth
• 2½ cups chopped chicken
• 1¼ cups frozen peas
• ½ cup heavy cream
• 2 sheets frozen store-bought puff pastry
• 1 egg
• 1 tablespoon water