Chocolate Mousse Cheesecake

For the crust:

1. Combine the crushed Oreo cookies and the melted butter. Press the mixture into the bottom and up the sides of a springform pan. Smooth out the mixture with the bottom of a measuring cup or glass. Wrap the bottom of the pan in a double layer of aluminum foil. Place the crust in the freezer while you make the cheesecake.

For the cheesecake layer:

1. In the bowl of a stand mixer (or large bowl with hand mixer), beat the cream cheese at medium speed until it is soft for about 4 minutes. With the mixer running, add the sugar and salt, and continue to beat another 4 minutes or so, until the cream cheese is light. Beat in the vanilla extract. Add the eggs one by one, beating for a full minute after each addition to yield a well-aerated batter. Reduce the mixer speed to low, and stir in the sour cream.
2. Give the batter a few stirs with a rubber spatula, just to make sure that nothing has been left unmixed at the bottom of the bowl, and scrape the batter into the springform pan. The batter should fill only half of the pan. Place the springform pan in a roasting pan. Pour boiling water into the roaster to come halfway up the sides of the springform pan.
3. Bake the cheesecake for 1 hour and 15 at which point the top will be lightly browned. Turn off the oven, and prop the oven door open with a wooden spoon. Allow the cheesecake to luxuriate in its water bath for another hour.
4. After 1 hour, carefully pull the roast pan/springform pan setup out of the oven, lift the springform pan out of the roaster—be careful, there WILL be some hot water in the aluminum foil—remove the foil. Let the cheesecake come to room temperature on a cooling rack.
5. When the cake is cool, cover the top lightly and chill the cake for at least 4 hours or overnight. Make the mousse once the cheesecake has cooled.

For the mousse:

1. Heat 1/2 cup cream in a small saucepan until just simmering.
2. 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.
3. 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.
4. Remove from the heat and stir in the chocolate chips, whisking until the mixture is smooth and the chocolate is completely melted. Whisk in 1/4 cup powdered sugar. Let the mixture cool to room temperature, whisking occasionally to avoid a skin forming across the top.
5. 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 and refrigerate.

For the ganache:

1. Combine 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 until ready to serve.