Preheat oven to
300 degrees. To make the crust, combine graham crackers, melted butter
and sugar in a medium bowl. Mix well with a fork to combine.
Press the mixture into the bottom of a 9-inch spring form pan that has been
coated with non-stick spray. Set aside.
To make the
filling, melt chocolate in a double boiler or medium bowl over simmering
water. Set aside to cool slightly.
In a large mixing
bowl, combine cream cheese, sour cream, egg, and vanilla. Mix on low
speed until smooth and creamy. Fold in sugar and flour. Pour
filling into prepared pan.
Drizzle melted
chocolate over surface of cheesecake. Using a toothpick swirl the
chocolate into the filling, just until decorative swirls form (don't
over-swirl, or you'll lose the effect).
Bake 1 hour, or
until center is set. Turn off oven, prop open the oven door (not all
the way, just slightly), and allow cake to cool 15 minutes. Transfer
pan to a wire rack and cool completely. Cover with plastic wrap and
refrigerate until ready to serve.