Melt the chocolate in a large heatproof bowl set over a saucepan filled with 1 inch of low simmering water, stirring occasionally until smooth. Remove from heat and cool for 5 minutes.
While the chocolate is melting Bend the Oreos in the food process until they are close to powdered but still a bit rough.
Melt the butter in a small cause pan or in the microwave until its a little more warmer than room temperature. Mix the butter and Oreo crumbs.
Line the bottom and sides of a springform pan with wax paper. Spread the Oreo mixture on the bottom of a springform pan.
Whip the heavy cream until it begins to thicken. Add the vanilla and whip for another 30 secs.
Gently fold slightly cooled chocolate (do not allow the chocolate to cool too much because it will begin to clump) into the whipped cream mixture.
Pour on top of the Oreo crust layer and refrigerate for at least 2 hours before serving.