Preheat oven to 350F. Grease a 9-inch tart pan or springform pan.
To prepare crust, mix Oreo cookies crumbs and melted butter in a small bowl, until a moist yet crumbly mixture forms. Firmly press the mixture into the bottom and sides of the pan.
Bake for 10 minutes. Let cool completely on a wire rack.
To prepare filling, cook sugar and eggs in a medium heat-proof set over a pot of barely simmering water, keep whisking until thick enough to coat the back of a spoon, about 5 minutes.
Stir the melted chocolate into the mixture until smooth. Remove from heat and set aside until completely cooled.
In the bowl of a standing mixer fitted with the paddle attachment, beat the butter until light and fluffy. Add the cooled chocolate mixture and continue beating until fully combined.
In another bowl, beat the cream and vanilla until it holds firm peaks. Reserve about half cup for garnish. Gently fold the remaining whipped cream into the chocolate mixture until incorporated and the mixture is light and fluffy.
Pour the mixture in the crust. Smooth the top with a spatula. Refrigerate the pies until set, at least 4 hours.
Remove pie from pan, top with the reserved whipped cream and shaved chocolate. Serve.