The short answer
Pastilla, also written bstilla, is a sweet and savoury pie of spiced pigeon or chicken and almonds, wrapped in paper-thin warqa pastry and dusted with icing sugar and cinnamon. It is the dish for a special meal. In Marrakech you find it at riad restaurants and many medina cafés, often in a chicken version.
In more detail
The surprise is the sugar. Under layers of crisp warqa pastry sits spiced meat, pigeon or chicken, with almonds. The top is dusted with icing sugar and cinnamon, so every bite is sweet, savoury and crisp at once. It is served in wedges and is rich, so it works best shared before or instead of a main course.
Several venues we keep notes on are known for it. Dar Justo in Mouassine serves a well-loved chicken pastilla from the rooftop of a boutique riad. Cafe Medina Rouge opposite the Koutoubia and Cafe Chez Zaza near Jemaa el-Fnaa both list it with their tagines and couscous. Chez Mohktar, a family-run canteen beside the Bab Doukkala mosque, serves chicken pastilla to a local crowd. Latitude 31 in Bab Doukkala serves a seafood version, and Ksar Essaoussan includes bstilla in its seven-course tasting menu.
La Maison Arabe plates pastilla in its courtyard salons, and its cooking school teaches the recipes served at the table. Pastilla is also the advanced dish in many cooking classes, since the pastry takes practice.