The chewy, rich filling for this dessert was inspired by gianduja, a chocolate-hazelnut paste created in Turin, Italy. The crust, made with whole-wheat flour, is simply pressed into the bottom of springform pan; its nuttiness pairs perfectly with the intense filling. If you like, dust the baked crostata with powdered sugar before serving, or top wedges with unsweetened whipped cream or crème fraîche. The crostata is best served the same day, but leftovers can be covered in plastic wrap refrigerated overnight; bring to room temperature before serving.