Prepare the crust: Preheat the oven to 325°F (163°C). Grease and line the bottom of a 9-inch springform pan. Combine the graham cracker crumbs, sugar, and melted butter in a medium bowl, press into the pan, and bake for 8-10 minutes. Set aside to cool.

1. Prepare the cranberry jam: Cook cranberries, sugar, water, and lemon juice over medium heat for 10 minutes, until cranberries burst and mixture thickens. Let cool to room temperature.
2. Prepare the white chocolate mousse filling: Melt the white chocolate in a double boiler or microwave, then cool slightly. Whip the heavy cream to stiff peaks. Beat the cream cheese, powdered sugar, vanilla, and sour cream, then fold in the white chocolate and whipped cream.
3. Assemble the cheesecake: Pour the white chocolate mousse over the cooled crust, smoothing the top. Drizzle cranberry jam on top and swirl with a knife to create a marbled effect. Refrigerate for 4 hours or overnight.
4. Serve and garnish: Before serving, garnish with whipped cream, fresh cranberries, and shaved white chocolate. Slice and serve chilled.