In the bowl of a stand mixer or a large bowl with a hand mixer, add the heavy cream, powdered sugar, cornstarch, vanilla, and cocoa powder. Begin by slowly stirring together until slightly thickened. Scrape down the sides of the bowl as needed.
Once slightly thickened, put the speed on medium and whip until soft peaks form. Set aside in the fridge until ready to assemble.
For the parfait assembly
Let the pie thaw overnight in the fridge. In a medium bowl, scrape out all of the pie filling into the bowl. Mix together so everything is combined and smooth, set aside.
Place the crust and the chocolate sandwich cookies into a gallon-sized zip baggie, crush using a rolling pin, or similar heavy item until crumbs form. Set aside.
To make it easier on yourself, place the cookies and cream filling into a piping bag. Place the chocolate whipped cream into a piping bag. Or, skip this step and fill glasses using a spoon. Take 8 small glasses and layer the different ingredients. I placed a layer of cookies and cream filling on the bottom, topped with cookie crumbs. Then, a thick layer of chocolate whipped cream and more cookie crumbs. Topped with more cookies and cream filling, a nice piped swirl of chocolate whipped cream, and a garnish of cookie crumbs for the final look. Feel free to layer however you wish!