For the crust, combine the Oreo cookie crumbs and the melted butter.
Press the mixture into the bottom and up the sides of a deep dish 9-inch pie plate.
Refrigerate while you make the cheesecake filling.
For the filling, with an electric mixer, blend together the softened cream cheese and granulated sugar until smooth.
Add the egg, egg yolk, and vanilla and mix until combined.
Blend in the sour cream.
Spread the filling over the cookie crust and bake for 40-45 minutes, until the edges are set and the center is slightly firm (you don't want it to be really jiggly).
Remove from the oven and let it cool completely on a wire rack.
For the mousse, heat 1/2 cup cream in a small saucepan until just simmering.
Place the egg yolks in a small bowl.
Whisking vigorously, pour a couple tablespoons of the hot cream into the egg yolks and continue whisking until completely combined.
Pour the tempered egg yolks into the saucepan with the remaining hot cream, whisking quickly the whole time, and return the saucepan to medium-low heat, cooking while stirring constantly, until the cream/egg mixture bubbles and thickens, 1-2 minutes.
Remove from the heat and stir in the chocolate chips, whisking until the mixture is smooth and the chocolate is completely melted.
For additional sweetness, whisk in up to 1/4 cup powdered sugar.
Let the mixture cool to room temperature, whisking occasionally to avoid a skin forming across the top.
When completely cool, beat the remaining 1/2 cup cream to stiff peaks and gently fold into the completely cooled chocolate mixture.
Spread the mousse over the top of the cooled cheesecake pie and refrigerate.
While the pie chills, make the ganache by combining the butter and heavy 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 glossy and smooth.
Stir in the vanilla and powdered sugar.
Spread the ganache over the mousse and refrigerate the pie for at least an hour and up to a day.