Place Oreo cookies in a food processor and pulse until finely ground. If you don't have a processor, place cookies in a zip-top bag and crush with a rolling pin until fine crumbs form.

Pour melted butter over the Oreo crumbs and stir until the mixture resembles slightly wet sand and holds together when pressed.

Press the crumb mixture firmly and evenly into the bottom and up the sides of a 9-inch pie dish. Use the back of a measuring cup to compact the crust for a clean edge.

Refrigerate the crust while preparing the mousse filling to allow it to set.

Place the chocolate chips and 3 tablespoons butter in a heat-safe bowl. Melt gently in the microwave in 15-20 second bursts, stirring between bursts, until smooth. Allow to cool slightly but not harden.

In a separate chilled bowl, whip the heavy cream with the powdered sugar and vanilla extract until soft peaks form using an electric mixer.

Gently fold the cooled melted chocolate into the whipped cream in 2–3 additions, using a spatula and folding motions to keep the mixture airy and mousse-like.

Spoon the chocolate mousse into the chilled Oreo crust, smoothing the top with an offset spatula.

Cover the pie and refrigerate for at least 4 hours, or overnight, until the mousse is set and sliceable.

Just before serving, garnish with extra whipped cream, chopped Oreos, and chocolate curls or drizzle if desired.