Heat oven to 350°F.
Crush crackers in plastic bag. Add sugar, ginger, nutmeg and cinnamon. Add butter; knead bag to blend. Press over bottom of 9-inch round springform pan.
Bake crust in 350°F oven 10 minutes. Cool on wire rack.
Beat cream cheese in bowl until smooth. Mix sugar, flour, nutmeg, cinnamon and cloves in small bowl. Add to cream cheese; beat until smooth. Beat in egg. Beat in eggnog in slow stream. Beat in vanilla. Pour into springform pan; tap pan lightly to release air bubbles.
Bake in 350°F oven 1 hour. Remove from oven; spread with sour cream. Bake 5 more minutes. Cool in pan on rack until cool to touch. Refrigerate until serving.
Melt chocolate in bowl over saucepan of simmering water. Add nutmeg. Line 8 x 4 x 3-inch loaf pan with foil. Pour chocolate into pan, spreading evenly; cool until firm. Lift out of pan. Make curls, using vegetable peeler. Arrange on top of cake. Reserve remaining bar for snacking.