Pumpkin Swirl Cheesecake

8 cinnamon graham crackers (each 5" by 2 1/2") or 1 cup graham-cracker crumbs
2 tablespoons margarine or butter (1/4 stick), melted
Three 8-ounce packages cream cheese, softened
1 cup sugar
2 teaspoons vanilla extract
4 large eggs
One 16-ounce can solid-pack pumpkin (not pumpkin-pie mix)
2 tablespoons cornstarch
1 teaspoon ground cinnamon
1/2 teaspoon salt

One 8-ounce container sour cream DIRECTIONS1. In food processor with knife blade attached or in blender at medium speed, blend graham crackers until fine crumbs form.2. Preheat oven to 325 degrees F. In 9" by 3" springform pan, with fork, stir graham-cracker crumbs and melted margarine or butter until moistened. With hand, press mixture onto bottom of pan. Bake crust 7 minutes. Cool completely in pan on wire rack.3. Meanwhile, in large bowl, with mixer at medium speed, beat cream cheese until smooth; slowly beat in sugar. With mixer at low speed, beat in vanilla extract, and eggs just until blended, scraping bowl often with rubber spatula.4. In medium bowl, mix pumpkin, cornstarch, cinnamon and salt. Stir half of cream-cheese mixture into pumpkin mixture until blended. Stir sour cream into remaining cream-cheese mixture.5. Reserve 1/2 cup pumpkin mixture. Pour remaining pumpkin mixture onto graham-cracker crust. Carefully pour cream-cheese mixture on top of pumpkin layer. Spoon dollops of reserved pumpkin mixture onto cream-cheese layer. With knife, cut and twist through cream-cheese layer to obtain swirl effect.6. Bake cheesecake 1 hour. Turn off oven; let cheesecake remain in oven 1 hour longer. Remove cheesecake from oven. With small knife, loosen cheesecake from side of pan to help prevent cracking during cooling. Cool completely in pan on wire rack. Cover and refrigerate cheesecake at least 6 hours or overnight until well chilled. Remove side of pan to serve.