For crust: in a medium bowl, mix together crumbs and butter until well blended. Press into a 9-inch spring form pan.

Preheat oven to 300F.

For filling: in a large bowl, beat together cream cheese, sugar, and eggs at medium speed until smooth and fluffy. Spoon half of this mixture into crust. Stir chocolate into remaining cream cheese mixture until well blended. Drizzle over batter in crust to make swirls.

Bake cake for 50 minutes. Transfer pan to wire rack and cool completely. Transfer cooled cheesecake to a serving plate, cover with plastic wrap and chill for 2 hours.

Uncover cheesecake; carefully remove from the pan.

For frosting: in a small bowl, mix together chocolate and sour cream. Spread over cake; chill briefly until frosting is set. Optional: shove as much cheesecake in your mouth as you can and then grin widely at your Mom as she takes your picture.