1. Preheat oven to 325°F. Mix crushed vanilla wafers, sugar, and melted butter until combined. Press into the bottom of a springform pan. Bake for 10 minutes. Let cool.

2. Beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well. Blend in vanilla and sour cream. Pour over crust and bake for 50–60 minutes, until center is set but slightly jiggly. Cool completely, then refrigerate for at least 4 hours or overnight.

3. Whisk milk, sugar, cornstarch, and egg yolks in a saucepan over medium heat. Stir constantly until thickened, about 7–10 minutes. Remove from heat and stir in butter and vanilla. Cool with plastic wrap touching surface to prevent skin. Once cool, spread gently over chilled cheesecake. Chill again.

4. Heat cream until just simmering. Pour over chopped chocolate and corn syrup. Let sit 2 minutes, then stir until smooth. Pour over custard layer and gently spread. Chill until set.