1. Preheat oven to 350 degrees F. For the crust: In a medium bowl, combine graham crackers and the 3 tablespoons sugar. Stir in melted butter. Press crumb mixture onto the bottom and 1 to 2 inches up the side of a 9-inch springform pan. Bake for 5 minutes. Cool on a wire rack while preparing filling.
2. For the filling: In a large bowl, combine cream cheese, the 1-1/3 cups sugar, the orange juice concentrate, and the 1 teaspoon vanilla. Beat with an electric mixer on medium speed until smooth. Stir in eggs and orange peel just until combined.
3. Pour filling into crust-lined pan. Place springform pan in a shallow baking pan. Bake for 40 to 45 minutes or until a 2-1/2-inch-wide area around the outside edge appears set when gently shaken. Remove springform pan from oven and set on a wire rack.
4. Meanwhile, stir together sour cream, the 1 tablespoon sugar, and the 1/2 teaspoon vanilla. Carefully spread sour cream mixture over the hot cheesecake.
5. Cool in springform pan on wire rack for 15 minutes. Using a small thin knife, loosen crust from side of pan. Cool for 30 minutes more. Remove side of the pan. Cool for 2 hours. Cover and chill for at least 4 hours or up to 24 hours.
6. If desired, garnish cheesecake with orange peel strips and kumquats.
7. Makes 12 to 16 servings.
8. To bake ahead: Transfer cooled cheesecake (whole or pieces) to a freezer bag; seal. Freeze whole cheesecake for up to 1 month or pieces for up to 2 weeks. Thaw whole ccheeseake in the refrigerator overnight or pieces at room temperature for 30 minutes.