Black-and-White Bars

Directions

1. 1
   TO MAKE THE CHOCOLATE WAFER CRUST: Line the bottom and sides of a 9 by 13-inch baking pan with heavy-duty aluminum foil.
2. 2
   Using a pastry brush, lightly coat the foil-lined pan with melted butter.
3. 3
   In the work bowl of a food processor fitted with the metal blade, process the chocolate cookies into crumbs (or put the cookies between 2 layers of waxed paper and crush with a rolling pin).
4. 4
   Combine the remaining melted butter (you should have at least 7 tablespoons) with the cookie crumbs.
5. 5
   Press the crumb mixture evenly over the bottom of the foil-lined pan.
6. 6
   TO MAKE THE CHEESECAKE FILLING: Preheat the oven to 300F.
7. 7
   In a large metal bowl set over a pan filled with 2 inches of simmering water, melt the dark chocolate, stirring occasionally, until smooth.
8. 8
   Remove from the heat and stir in the cream.
9. 9
   Using an electric mixer fitted with the paddle attachment, beat the cream cheese and the 1 cup sugar on medium speed until smooth.
10. 10
    Beat in the egg yolks, 1 at a time, scraping the sides of the bowl frequently with a rubber spatula.
11. 11
    Add the chocolate-cream mixture, vanilla, Kahlua, and salt and beat at medium speed for 2 minutes.
12. 12
    Using an electric mixer fitted with the whisk attachment and a clean bowl, whip the egg whites on high speed until firm peaks form.
13. 13
    Using a large rubber spatula, gently fold the egg whites into the chocolate-cream cheese mixture.
14. 14
    Spoon the filling evenly over the chocolate crumb crust.
15. 15
    Bake the bars for 30 minutes; the filling will rise and will be almost set.
16. 16
    Turn off the heat and leave the bars in the oven for 30 more minutes.
17. 17
    Transfer the baking pan to a wire rack to cool completely.
18. 18
    TO MAKE THE WHITE CHOCOLATE TOPPING: In a large metal bowl set over a pan filled with 2 inches of simmering water, melt the white chocolate, stirring until smooth.
19. 19
    Remove from the heat and slowly stir in the cream and the creme de cacao, if you wish.
20. 20
    Pour the mixture over the cooled cheesecake.
21. 21
    Freeze overnight, making sure you keep the pan level or the white chocolate topping will set unevenly.
22. 22
    When ready to serve, lift the foil out of the pan and set on a work surface.
23. 23
    Using a long, sharp knife, cut the cake into 1 1/2-inch-square bars.
24. 24
    Dip the knife in hot water and wipe it clean between cuts, or the bars lose their perfect black-and-white look.
25. 25
    The uncut cheesecake can be made up to 3 weeks in advance, wrapped, and frozen until ready to cut and serve.
26. 26
    Be sure to use real white chocolate made with cacao butter for the topping.
27. 27
    Some products labeled white chocolate include other, cheaper, and often unhealthier fats for the cocoa butter.
28. 28
    Read labels carefully to ensure you are getting the real thing.
29. 29
    I like Green & Blacks excellent organic white chocolate bar made with 30 percent cacao butter.