In a small saucepan, heat cream, corn syrup, orange zest and salt. Stir constantly with a wooden spoon, until mixture comes to a boil.

Place chopped chocolate in a heat-proof bowl. Pour hot cream over the chopped chocolate and let stand for one minute to melt the chocolate. Stir until smooth. Add orange liqueur and vanilla.

Cover surface with plastic wrap and freeze for two hours.

Line a large baking pan with Gefen Parchment Paper or a Silpat. Dust pan with a light coating of cocoa.

Use a one-inch scoop to form small balls of truffles mixture and drop onto the prepared pan. Dust your hands with cocoa to keep truffles from sticking to your fingers.

Cover with plastic and freeze 30 minutes more. You should have approximately 25 truffles.

Wrap the outside of a nine- or 10-inch springform with heavy-duty foil, making sure the foil extends beyond the top of the pan.

Mix the crushed cookies with the butter until thoroughly combined. Press firmly into the bottom of the prepared pan. Freeze until needed.

Preheat oven to 325 degrees Fahrenheit.

In a large bowl, beat the softened cream cheese for 20 to 25 seconds, just until creamy. Add sugar, orange zest and corn starch. Mix just until combined, for 10 to 15 seconds. Add sour cream, liqueur and vanilla. Mix again for 10 to 15 seconds, scraping down sides of the bowl.

Beat eggs in a small bowl. With mixer running, add eggs and mix just until combined. Do not overmix; this will incorporate too much air in the batter and cause cracks during baking.

Pour half the batter into cooled crust. Remove truffles from the freezer and arrange 16 in a circle in the batter at the outer edge of the pan. Arrange nine more truffles in another circle just inside the first one. Do not put any truffles in the center. Pour remaining cheesecake batter into the pan.

Put the springform into a large roaster. Pour hot water into the roaster until it reaches halfway up the sides of the springform. Bake 70 to 80 minutes, until top is firm around the edges and the center is still jiggly. Turn off oven and allow cake to rest in warm oven for 45 minutes longer. Remove springform from roaster and run a spatula or knife around the edge of the cake.

Chill thoroughly, for five to six hours.