Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.

In a food processor, pulse the Oreo cookies into fine crumbs. In a mixing bowl, combine these crumbs with melted butter until the mixture resembles wet sand.

Press the mixture into the bottom of the prepared pan and bake for 10 minutes until set; then cool completely.

Using a stand mixer, whip the heavy cream on medium speed, gradually adding powdered sugar until firm peaks form.

In a double boiler, melt the semi-sweet chocolate chips with remaining butter until smooth.

In a large bowl, beat the cream cheese until smooth. Add powdered sugar, cocoa powder, vanilla extract, and salt.

Fold in the cooled chocolate mixture until well-integrated.

Fold half of the whipped cream into the chocolate mixture, and then fold in the remaining whipped cream.

Spread the chocolate filling over the cooled Oreo crust and smooth the top with a spatula.

Cover and refrigerate for at least 3 hours or overnight.

Whip additional cream until soft peaks form and spread over the chilled bars, then top with chocolate shavings.

Lift the bars out using parchment paper, cut into portions with a hot, damp knife, and serve cold.