3/4 cup graham cracker crumbs
1 tablespoon plus 2/3 cup sugar, divided
1 teaspoon grated grapefruit zest
1/4 teaspoon ground ginger
2-1/2 tablespoons butter, melted
2 packages (8 ounces each) cream cheese, softened
1/2 cup sour cream
2 tablespoons pink grapefruit juice
2 large eggs, lightly beaten
Fresh citrus fruit, optional
1.Place a greased 6-in. springform pan on a double thickness of heavy-duty foil (about 12 in. square). Wrap foil securely around pan. Pour 1 in. water into a 6-qt. slow cooker. Layer two 24-in. pieces of foil. Starting with a long side, fold up foil to create a 1-in.-wide strip; roll into a coil. Place in slow cooker to form a rack for the cheesecake.
2.In a small bowl, mix cracker crumbs, 1 tablespoon sugar, zest and ginger; stir in butter. Press onto bottom and about 1 in. up sides of prepared pan.
3.In a large bowl, beat cream cheese and remaining sugar until smooth. Beat in sour cream and grapefruit juice. Add eggs and beat on low speed just until combined.
4.Pour into crust. Place springform pan on top of coil. Cover slow cooker with a double layer of paper towels; place lid securely over towels. Cook, covered, on high 2 hours. Do not remove lid; turn off slow cooker and let cheesecake stand, covered, in slow cooker 1 hour. Center of cheesecake will be just set and top will appear dull.
5.Remove springform pan from slow cooker; remove foil from pan. Cool cheesecake on a wire rack 1 hour. Loosen sides from pan with a knife. Refrigerate overnight, covering when completely cooled. Remove rim from pan. If desired, garnish with fruit.
Top cheesecake with orange and grapefruit sections (from half an orange and half a grapefruit) and kumquat slices.