Begin by crushing your digestive biscuits or graham crackers into fine crumbs using a food processor or a rolling pin. In a mixing bowl, combine the crumbs with melted unsalted butter, stirring until the mixture resembles wet sand. Press this mixture firmly into the base of a springform pan, creating an even layer. Place the pan in the refrigerator for about 30 minutes to allow the crust to set and firm up.

While the crust chills, take a cold mixing bowl and beat the heavy whipping cream with powdered sugar using an electric mixer. Whip the cream on medium speed until soft peaks begin to form, about 3-5 minutes. Set the whipped cream aside in the fridge to keep it cool.

In another mixing bowl, combine softened cream cheese and Nutella, blending them together until completely smooth. Gently fold in the mashed ripe bananas and a splash of vanilla extract, mixing until well incorporated. Carefully add the whipped cream to this mixture, folding it in gently.

Pour the cheesecake filling over the chilled crust, smoothing it out evenly. Once assembled, cover the cheesecake and refrigerate for at least four hours, or preferably overnight, to allow it to set properly.

Just before serving, garnish the cheesecake with banana slices, a drizzle of Nutella, and a sprinkle of cocoa powder or chopped nuts. Slice and serve chilled.