(adapted from Baking Illustrated)
Graham Cracker Crust
5 tablespoons unsalted butter, melted
8 whole graham crackers, crushed (we used chocolate graham crackers)
1 tablespoon sugar
2 1/2 pounds (five 8-ounce packages) cream cheese, cut into rough 1-inch chunks, at room temperature
1/8 teaspoon salt
1 1/2 cups sugar
1/3 cup sour cream
2 teaspoons juice from 1 lemon
2 teaspoons vanilla extract
2 large egg yolks plus 6 large eggs, at room temperature
4 ounces bittersweet chocolate
FOR THE CRUST
Adjust an oven rack to the lower-middle position and heat the oven to 325 degrees. Generously grease the bottom and sides of a 9-inch springform pan. Combine the graham cracker crumbs, sugar, and melted butter in a medium bowl and mix until evenly moistened. Empty the crumbs into the springform pan and press evenly into the pan bottom, a small ramekin works well for this. Bake until fragrant and beginning to brown around the edges, about 13 minutes. Cool while preparing the filling.
FOR THE CHEESECAKE FILLING
Increase the oven temperature to 500 degrees. In the bowl of a standing mixer, beat the cream cheese at medium-low speed to break up and soften it slightly, about 1 minute. Scrape the beater and the bottom and sides of the bowl well with a rubber spatula; add the salt and about half of the sugar and beat at medium-low speed until combined, about 1 minute. Scrape the bowl; beat in the remaining sugar until combined, about 1 minute. Scrape the bowl; add the sour cream, lemon juice, and vanilla, and beat at low speed until combined, about 1 minute. Scrape the bowl; add the egg yolks and beat at medium-low speed until thoroughly combined, about 1 minute. Scrape the bowl; add the remaining eggs 2 at a time, beating until thoroughly combined, about 1 minute, scraping the bowl between additions. Reserve 1 cup of the filling.
Melt the bittersweet chocolate in a heatproof bowl. Add 1 cup of the cheesecake filling to the melted chocolate; mix until no white streaks remain. Spoon the chocolate cheesecake mixture into a pastry bag fitted with a round tip. Set aside.
Grease the sides of the springform pan, again. Set the springform pan on a rimmed baking sheet (to catch any spills if the pan leaks). Pour the filling into the cooled crust. To make the polka dots, insert the tip of the pastry bag about 1/2-inch into the cheesecake and squeeze the bag to make a sphere. Continue in a random pattern around the cheesecake until all the chocolate mixture is used up.
Bake 10 minutes; without opening the oven door, reduce the oven temperature to 200 degrees and continue to bake until the center of the cheesecake reads about 150 degrees, about 1/2 hour in our oven. Transfer the cake to a wire rack and cool until barely warm, 2 1/2 to 3 hours. Run a paring knife between the cake and the springform pan sides. Wrap tightly in plastic wrap and refrigerate until cold, at least 3 hours.
To unmold the cheesecake, remove the sides of the pan. Slide a thin metal spatula between the crust and bottom of the pan to loosen, then slide the cake onto a serving plate. Let the cheesecake stand at room temperature about 30 minutes, then cut into wedges and serve.