Bake for 60-70 minutes or until the center reaches 200F. You can also test by lightly tapping the center surface of the pie - it should spring back when done. Loosely cover the pie with foil after 40 minutes to prevent the crust from over browning. Let cool on a wire rack for 2 hours before serving.
To prepare the whipped cream
Beat the whipping cream, cocoa powder, and powdered sugar together until med-stiff peaks. Serve with each slice of pie.