- Prepare crust: 
- Mix graham cracker crumbs, sugar, and melted butter 
- Press into bottom of springform pan 
- Bake at 325°F for 10 minutes 
- Cool completely 
- Cheesecake layer: 
- Beat cream cheese and sugar until smooth 
- Add eggs one at a time 
- Mix in sour cream and vanilla 
- Pour over crust 
- Bake at 325°F for 1 hour 
- Cool completely 
- Custard layer: 
- Whisk milk, sugar, cornstarch in saucepan 
- Cook until thickened 
- Temper egg yolks, then add to mixture 
- Cook until very thick 
- Cool completely 
- Spread over cheesecake layer 
- Chocolate ganache: 
- Heat cream until just simmering 
- Pour over chocolate 
- Let sit 5 minutes, then whisk until smooth 
- Pour over custard layer 
- Refrigerate 4 hours before serving