For the crust: Preheat oven to 325°F. Prepare an 8-inch springform pan with pan spray.
In a medium bowl, stir together graham cracker crumbs and sugar. Add the melted butter and mix well to combine.
Spread the graham cracker mixture into the bottom of the pan. Press evenly on the bottom and 1 inch up the sides of the pan. Reserve.
For the filling: Using an electric mixer, whisk together the egg whites, vanilla extract, corn syrup, and sugar until well blended – approximately 2 minutes. Reserve.
In a large mixing bowl, blend the cream cheese on low speed until smooth and creamy. Add one egg yolk at a time, beating well after each addition. Slowly add the egg white mixture into the cream cheese mixture on lowest speed until incorporated. Scrape down the sides of the bowl as needed.
Place unsweetened chocolate, semi-sweet chocolate, and butter in a stainless steel bowl. Place bowl over a saucepan of simmering water (do not allow bottom of bowl to touch water). Stir chocolate frequently with a whisk until completely melted. Remove from heat. You can also melt chocolate in the microwave in a microwave-safe bowl at 10-second intervals, stirring occasionally, until chocolate is melted.
Add 1 cup of the cheesecake batter to the melted chocolate mixture. Add the liqueur and mix until well blended – approximately 1 minute.
Pour the non-chocolate cheesecake batter into the springform pan. Pour chocolate batter in a spiral pattern onto the cheesecake batter. Take a toothpick or tip of a small knife and make tiny spirals an inch deep to give the cake a swirl pattern. Do not over swirl or the cake will loose the pattern effect.
Bake in a water bath in center of oven until the cake is set – approximately 70 minutes. Let cake cool to room temperature before placing in the refrigerator. Chill in the refrigerator at least 8 hours or overnight before serving.
Loosen the cheesecake by running a knife around the inside edge of the springform pan. Remove ring and place cheesecake on serving dish. Use a knife dipped in hot water to cut. Serve.
Chef’s Technique for Water Bath: To create a water bath, use a large baking pan such as an 11 x 15 roasting pan. Place springform pan into the larger pan and place in oven. Very carefully pour boiling water into the larger pan until it reaches halfway up the side of the springform pan.