Instructions

1. 1
   Place rack in center of the oven. Preheat oven to 150 °C (300 °F).
2. 2
   If starting with whole cookies, crackers, or wafers, place them in a sturdy plastic bag a few at a time and crush using a rolling pin, or grind using a food processor.
3. 3
   Mix together chocolate crumbs and melted butter.
4. 4
   Press crumb mixture into bottom and sides of 9-inch springform pan.
5. 5
   In a large bowl, beat together sugar and eggs at medium speed, slowly adding cream cheese, until smooth and fluffy.
6. 6
   Spoon half of cream cheese mixture into crust.
7. 7
   Melt 4 ounces of chocolate using a double boiler or, with care, a microwave. Stir into remaining cream cheese mixture until well blended.
8. 8
   Drizzle chocolate cream cheese mixture over batter in crust. Draw a spoon or other implement through the batter a few times to make swirls. Spread evenly.
9. 9
   Bake cheesecake for 50 minutes. After the first 30 minutes has gone by, place aluminum foil on top to prevent cracking and scorching.
10. 10
    Cool completely.
11. 11
    Cover with plastic wrap, and chill for about 2 hours or up to several days.
12. 12
    Transfer cheesecake to a serving plate.
13. 13
    Uncover cheesecake; carefully remove side of pan.
14. 14
    Melt remaining chocolate.
15. 15
    Mix with sour cream.
16. 16
    Spread over cake, and chill to set.