Chill the mixing bowl and beaters for 15–20 minutes.
Pour cold heavy cream, powdered sugar and vanilla into bowl; whip until stiff peaks form.
Line a 9×13 (or 8×8) pan (optionally with parchment paper).
Spread a thin layer of whipped cream at bottom.
Arrange a layer of Oreos on top (break a few to fit if needed).
Spread about ⅓ of the whipped cream over the Oreos.
Add a second layer of Oreos.
Spread remaining whipped cream over top, smoothing the surface.
Cover tightly and refrigerate for at least 6–8 hours (overnight recommended).
To serve: warm a knife under hot water, dry it, slice, and optionally top with crushed Oreos or chocolate shavings.