Blend Oreo cookies into fine crumbs using a food processor. Melt salted butter and mix with Oreo crumbs. Firmly press mixture into the bottom and sides of a springform pan. Chill the crust in the refrigerator for at least 30 minutes.

In a medium saucepan, whisk together granulated sugar, cornstarch, and cocoa powder. In a separate bowl, combine half and half with egg yolks. Gradually whisk the egg mixture into the dry ingredients. Cook over medium heat until thickened, about 5-7 minutes. Remove from heat and incorporate butter, semisweet chocolate, and vanilla extract until smooth.

Pour the chocolate filling into the chilled Oreo crust, spreading evenly. Cover and refrigerate for a minimum of 6 hours or overnight.

Combine cold heavy cream, powdered sugar, and vanilla extract in a mixing bowl. Beat until stiff peaks form. Optionally, add cornstarch to stabilize your topping.

Spread whipped cream over the chocolate filling and sprinkle with crushed Oreos or chocolate shavings. Slice and serve.