½recipe Magpie Dough for Flaky Piecrust(recipe follows), chilled overnight
2cups(270 g) Nutella
12ounces(340 g) cold mascarpone cheese
1cup(237 ml) heavy cream
Lightly sweetened freshly whipped creamfor serving if desired
Lightly flour a smooth work surface and a rolling pin.
Take a chilled disk of dough out of the fridge. Give it a couple of firm squeezes, then unwrap it and set it on the floured work surface.
Set the pin crosswise on the dough and press down firmly, making a nice deep channel across the full width of the disk. Turn the disk 180 degrees and repeat, making a second indentation, forming a plus sign.
Use your rolling pin to press down each of the wedges, turning the dough 45 degrees each time. This will give you the beginnings of a thick circle.
Now, rolling from the center outward and rotating the dough a quarter turn to maintain a circular shape, roll the dough out to a 13-inch circle with an even thickness of ¼ inch.
Set your 9-inch (23-cm) pie pan alongside the circle of dough. Brush off any loose flour, carefully fold the dough circle in half, transfer it to the pan, and unfold.
At this point, the dough will be lying across rather than fitted into the pan. Now, without stretching the dough, set the dough down into the pan so that it is flush up against the sides and bottom. The best way to do this is to gingerly lift the dough and gently shift it around so that it settles into the pan bit by bit. Use a very light touch to help cozy it in.
To flute the edge, fold the overhang under to form a 1-inch wall that rests on the lip of the pan with the seam slightly below the pan’s top edge. Flute the edge of the crust at about 1-inch intervals, pressing from the inside with the knuckle of your index finger while supporting on the outside with the thumb and index fingers of your opposite hand.
Transfer the crust to the refrigerator to chill while you make your filling or to the freezer to prepare it for prebaking. Alternatively, at this point the crust can be covered tightly in plastic wrap and refrigerated for up to 3 days or double-wrapped and frozen for up to 2 months (defrost overnight in the refrigerator before filling and baking or prebaking, or at room temperature for 30 minutes).
To prebake the shell, chill the panned, fluted piecrust in the freezer until firm, 15 to 20 minutes.
Preheat the oven to 375°F with the rack in the center. Line a rimmed baking sheet with parchment paper or foil. Cut an additional 13×13-inch square of parchment.
Set the pan on the lined baking sheet. Set the square of parchment in the pie shell and gently smooth it into place, pleating as needed to fit it up against the bottom and sides of the shell. The edges of the paper will project beyond the rim of the pan; just leave them standing straight up.
Fill the shell to the top with dried beans. Slide the baking sheet into the oven and bake the shell for 25 minutes.
Set out a wire rack and alongside it, a mixing bowl. Take the baking sheet out of the oven and set it on the rack; bring together the points of the parchment, and carefully lift out the beans and transfer them to the bowl.
Slide the baking sheet back into the oven and bake the crust another 10 minutes (until golden brown and fully baked–mine baked twice as long, an extra 20 minutes until the bottom of the crust was light golden). Cool completely on a wire rack.
Combine the Nutella, mascarpone, and salt in a large bowl and use an electric mixer on medium-low speed to beat together until smooth and shiny, 3 to 5 minutes.
Whip the cream to medium peaks.
Fold the whipped cream into the Nutella mixture until no white streaks remain.
Scoop the mousse into the prepared pie shell and smooth the top. Cover with plastic wrap and refrigerate overnight (at least 8 hours or up to 3 days) before slicing and serving.
Serve cold, topped each slice with whipped cream, if desired.