Crush Oreos. Add gluten-free Oreo cookies to a food processor and pulse to crush to fine crumbs. (Alternatively, you can put the cookies in a gallon-size zip top bag and crush them with a rolling pin)

Add Butter To Crumbs. Pour the melted butter over the cookie crumbs and pulse or stir to coat the crumbs evenly with butter.

Pat Out Crust. Transfer the cookie crumb mixture to the pie pan. Use the back of a measuring spoon or flat-bottomed cup to gently pat out the crust into an even layer along the bottom and up the sides of the pie pan.

Bake & Cool Crust. Place the crust in the oven and bake for 8-10 minutes. Remove from the oven and cool the crust on a wire rack while you make the filling. (Crust can be made a day in advance and stored at room temperature)

Combine Dry Ingredients. In a medium saucepan, combine cornstarch, cocoa powder, sugar, and salt. Whisk to combine well.

Add Milk & Cook To Thicken. Next, pour in the milk and whisk to combine, stirring over medium heat until the mixture comes to a simmer. At first, it will seem like the cocoa powder mixture isn't going to blend in, but as the milk heats up, it will dissolve the cocoa until the mixture is smooth. Whisk constantly to avoid lumps. It's VERY important to get the filling to thicken enough that you can see the tracks the whisk makes in the pudding. If you don't thicken the pudding at this stage, it will not set up later.

Finish The Pudding. Remove the pan from the heat and immediately stir in the butter, chocolate, and vanilla. Whisk to combine until the mixture is completely smooth and the chocolate has melted. (If you do have any lumps in the chocolate mixture at this point, you can press the pudding through a fine mesh strainer to strain them out.)

Pour Filling Into Crust. Working quickly (so the pudding doesn't form a "skin" on the top), pour the warm pudding into the cooled baked crust. Smooth out the top with a spatula.

Cover And Chill. Cover the pie with plastic wrap, pressing the plastic wrap down onto the pudding (Again, this helps prevent a skin from forming on the top of the pie). Chill at least 2-3 hours, or until chilled through. (You can prep this pie up to a day in advance, if needed.)

Start Beating The Cream. Add heavy cream to a large glass or metal mixing bowl (or the bowl of a stand mixer). Whip the cream with the whisk attachment or a handheld electric mixer for 2-3 minutes, until it starts to get foamy.

Stabilize & Finish The Whipped Cream. Add powdered sugar and vanilla extract, then whip the cream on high speed about 4-5 minutes, or until it has doubled in volume and you reach stiff peaks. (The whipped cream will show the path of the beaters as it mixes, and the whipped cream should hold its shape if you dip a spoon into it and rotate it around.) The whipped cream can be chilled up to a day in advance at this point, if needed.

Decorate The Pie. When you're ready to serve the pie, remove the plastic wrap from the pie and top with whipped cream. (You can dollop or pipe the whipped cream onto the pie.) Garnish with chocolate curls, shaved chocolate, crumbled cookie crumbs or your favorite garnishes--chopped toasted nuts, toffee bits, etc.

Serve & Store. Chill the pie until you're ready to serve, then cut into slices and enjoy. Leftover pie can be covered and stored in the fridge up to 3 days. (This pie does not freeze well.)