In another bowl, cream the butter, the sugar, and cocoa powder in an electric mixer. Add the egg and vanilla and beat until smooth. At low speed or with a wooden spoon, stir in the dry ingredients. Form a disc with the dough. Cover with plastic wrap. Refrigerate for 30 minutes.
On a floured work surface, roll out the pastry and line a 23-cm (9-inch) pie plate with removable bottom.
With the rack in the lowest position, preheat the oven to 200 °C (400 °F). Bake for about 15 minutes or until the crust is thoroughly cooked.
In a small saucepan, bring the cream, mashed bananas, and brown sugar to a boil.
In a food processor, pour the hot cream over the chocolate. Pulse for a few seconds at a time, until the chocolate has melted. Add the egg and pulse until the mixture is smooth. Spread the ganache into the crust. Refrigerate for 3 hours or until the filling is firm.
In a bowl, beat all the ingredients with an electric mixer until stiff peaks form.
Cover the pie with the whipped cream and top with chocolate shavings. Refrigerate until ready to serve.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.