Oreo Crust: Add whole Oreo cookies to a food processor and pulse until very fine crumbs. Stir in the melted butter. Pour mixture into a 9-inch springform pan. Use the back of a measuring spoon to press it firmly into the bottom and half way up the sides of the pan. Refrigerate while you make the cheesecake filling.

Preheat the oven to 325 degrees F.

Cheesecake: Cream together the softened cream cheese and granulated sugar until well blended. Add the eggs, egg yolk, and vanilla and mix. Mix in the sour cream. Spread the filling over the Oreo cookie crust into an even layer.

Bake at 325 degrees F for 45-60 minutes, or until the edges are set and the center is slightly firm (it may jiggle just slightly).Remove from oven and allow to cool completely. (No need to use a water-bath, since we will add a mousse and ganache on top).

Mousse: Add chocolate chips to a heatproof bowl. In a separate microwave safe bowl (or in a saucepan on the stove), heat 1/2 cup cream until hot (not boiling). Pour hot cream over chocolate chips, and set aside for a few minutes, to allow the chocolate to warm. Then stir until smooth. Allow to cool completely.

Add remaining 1/2 cup cream and vanilla to a mixing bowl and whisk until stiff peaks. Gently fold in to cooled melted chocolate mixture. Spread the mousse over the top of the cooled cheesecake. Refrigerate for at least 3-4 hours, or overnight.

Ganache: Place chocolate chips in a small bowl. Add butter and cream to a saucepan over medium heat. Bring to a simmer. Pour the hot cream mixture over the chocolate and stir until melted and smooth. Stir in vanilla and powdered sugar. Pour the ganache over the chilled cheesecake.

Refrigerate again for at least an hour before serving