Black and White Cheesecake

Crust:
3/4 stick (6 tablespoons) unsalted butter
1/2 cup sugar
3/4 teaspoon vanilla extract
1/8 teaspoon salt
1/4 cup plus 2 tablespoons sifted unsweetened cocoa powder
3/4 cup all-purpose flour

Filling:
5 ounces bittersweet chocolate, cut into bits
1/4 cup water
24 ounces cream cheese, slightly softened
1 1/4 cups sugar
1/2 teaspoon vanilla extract
2 large eggs

To make the crust, mix the butter, sugar, vanilla, and salt in the bowl of a food processor and whirl until creamy. Add the cocoa and process until you have a dark, smooth paste. Add the flour and pulse just until incorporated but still crumbly.

Firmly pat three-fourths of the mixture into the bottom of an 8-inch springform pan or cheesecake pan with a removable bottom. With a fork toss and spread the remaining one-fourth crumbly dough loosely in a shallow baking pan. Place both the bottom crust and the pan of extra dough in a preheated 350-degree oven. Bake for 10 minutes. Remove the baked crumbs. Bake the bottom crust for an additional 5 minutes. Let crust and crumbs cool completely on a rack. Reduce the oven temperature to 325 degrees.

Pulverize the cooled crumbs. Store in an airtight container until needed.

To make the filling, melt the chocolate with the water in a double boiler, stirring occasionally until the chocolate is melted and smooth. Or, microwave on medium for 1 minute. Stir until smooth and keep warm.

Place the cream cheese in the bowl of an electric mixer and beat on medium speed, gradually adding the sugar, until completely smooth. Add the vanilla and the eggs, one by one, beating only until well mixed.

Measure and set aside 1 cup of the cheesecake filling. Pour the remaining batter over the baked chocolate crust; set aside.

Stir the warm chocolate into the reserved cheesecake batter. Pour the chocolate batter in a thick ring, about 1/2 inch in from the side of the pan, on top of the plain batter. Use a soup spoon to marble the chocolate. Try not to blend the batters together too much. If necessary, use your finger to wipe the side of the pan clean above the batter after marbling.

Bake in the 325-degree oven for 20 to 25 minutes, or until the cheesecake shows signs of puffing around the edges but is still very soft in the center. Remove the cake from the oven and run a thin knife blade carefully around the edges to release the cake from the side of the pan.

Cool in the pan, on a rack, covered with an inverted large mixing bowl. Refrigerate, covered with plastic wrap, after it is completely cool. The cake may be made to this point and refrigerated up to 4 days in advance. Unmold the cheesecake. Press reserved cookie crumbs around the sides of the cake, being careful not to get the crumbs on top.