Preparation Steps

• Heat the oven to 400°F. In a small saucepan or microwave-safe cup, gently warm the milk until steaming but not boiling; keep it nearby (warm milk helps the sauce stay silky).
• Start the filling: In a wide skillet over medium heat, melt 2 tablespoons of the butter. Add the onion and carrot with a pinch of salt. Cook, stirring often, until the onions are translucent and the carrots soften slightly, 5 to 6 minutes.
• Add the remaining 1 tablespoon butter and the mushrooms. Increase heat to medium-high and cook until the mushrooms release their liquid and take on some color, 6 to 8 minutes. Stir in the black pepper and poultry seasoning.
• Sprinkle the flour evenly over the vegetables and cook, stirring, for 1 to 2 minutes to form a roux. Pour in the dry sherry and let it bubble for 30 seconds, scraping the pan.
• Gradually whisk in the warm milk and add the kosher salt. Bring to a gentle simmer and cook, stirring, until the sauce is smooth and slightly thick, about 3 to 5 minutes.
• Fold in the peas, pimientos, and shredded chicken. Simmer 2 minutes more, then take off the heat, cover, and let the mixture rest 5 minutes to thicken. Stir in half the parsley and keep warm on low.
• While the sauce cooks, arrange the frozen puff pastry shells on a parchment-lined baking sheet. Bake at 400°F until well risen and deeply golden, 22 to 25 minutes. Let stand 5 minutes, then lift off the caps and gently remove any soft centers to make room for the filling.
• Spoon the hot chicken mixture into the warm pastry shells. Top with the caps and sprinkle with the remaining parsley. Serve at once.