Place Oreo cookies in a food processor and pulse until small crumbs. Stir in the melted butter.
Press the mixture into a deep dish 9-inch pie plate, covering the bottom and up the sides of the dish. Refrigerate while you make the filling.
For the Cheesecake Filling:
Cream together the softened cream cheese and granulated sugar until well blended.
Add the egg, egg yolk, and vanilla and mix. Blend in the sour cream.
Spread the filling over the Oreo cookie crust in an even layer.
Bake at 325 degrees F for 40-45 minutes, or until the edges are set and the center is slightly firm (it can be a little soft, just not jiggly). Remove from oven and allow to cool completely.
For the Chocolate Mousse:
Heat 1/2 cup cream in a small saucepan until just simmering.
Whisk the egg yolks together in a small bowl. Add a big spoonful of the hot cream into the egg yolks and continue whisking until combined. Repeat with another spoonful of hot cream, whisking well to combine.
Pour the tempered egg yolks into the saucepan with the remaining hot cream, whisking constantly over medium-low heat, and cook until the mixture bubbles and thickens, 1-2 minutes.
Remove from the heat and stir in the chocolate chips, stirring constantly until the chocolate is completely melted and the mixture is smooth.
Allow mixture to cool to room temperature, whisking occasionally to avoid a skin forming across the top.
Once cooled, beat the remaining 1/2 cup cream to stiff peaks and gently fold it into the chocolate mixture.
Spread the mousse over the top of the cooled cheesecake pie and refrigerate.
For the ganache:
While the pie chills, make the ganache. Combine the butter and cream in a saucepan over medium heat until the butter is melted and the mixture is simmering.
Place the chocolate in a small bowl. Pour the hot cream mixture over the chocolate and stir until melted and smooth.
Add the vanilla and powdered sugar and stir well. Pour the ganache over the mousse.
Refrigerate cheesecake until ready to serve (at least an hour - the pie can be made up to a day in advance).