Marble Cheesecake Bars

1. 1
   Heat the oven to 325°F and arrange a rack in the middle.
2. 2
   Coat a 13-by-9-inch pan with butter. Place cookie crumbs and melted butter in a medium bowl and mix until thoroughly combined. Pour the crumb mixture into the pan and, using the bottom of a cup, press evenly into the bottom and slightly up the sides.

For the filling:

1. 1
   Combine chocolate and butter in a small saucepan and cook over low heat, stirring frequently, until evenly melted. Remove from heat and let cool to room temperature, about 15 minutes.
2. 2
   Whisk together sugar and flour in a medium bowl and set aside. Place cream cheese in the bowl of a stand mixer fitted with a paddle attachment and beat on medium speed until smooth, about 1 minute. With the mixer running, pour in sugar-flour mixture and beat until incorporated. Stop the mixer to scrape down the sides of the bowl and the paddle.
3. 3
   With the mixer on low, add vanilla and then 1 egg, allowing to incorporate completely. Stop the mixer to scrape down the sides of the bowl and the paddle. Return the mixer to low and repeat with remaining 2 eggs, allowing each to incorporate completely before adding the next.
4. 4
   Pour 2 3/4 cups of batter from the mixer into a medium bowl and reserve. Add cooled chocolate to the remaining batter in the mixer and beat on medium speed until evenly incorporated.
5. 5
   Randomly drop spoonfuls of chocolate batter over the prepared crust, then drop spoonfuls of reserved vanilla batter in between the chocolate. Drag a knife through the batter in a figure eight to create a marbled pattern. Bake until the outer 1 inch of batter is set and puffed but the center is slightly jiggly, about 25 to 30 minutes. Remove to a rack and let cool completely. Refrigerate until well chilled and firm, about 1 to 2 hours. Cut into squares and serve.