Preheat the oven to 140 C / Gas 1. Cover the bottom of a 23cm springform cake tin with foil and snap the base plate into the ring. Grease the sides of the tin with butter.
Process biscuits in a food processor until they break up into fine crumbs. Transfer to a bowl and add butter; use a fork to blend. Press crumb mixture into the bottom of the tin. Top the biscuit base with 1/2 the figs and 100g chopped hazelnuts.
Place cream cheese in a large bowl and beat using an electric mixer on low speed for 5 minutes, scraping the sides of the bowl. Sift sugar and flour together in a bowl and add to the cream cheese mixture. Add soured cream, buttermilk, vanilla extract and hazelnut liqueur; beat thoroughly. Add eggs 1 at a time and mix on low speed until yolks disappear. Pour mixture into the prepared tin.
Bake in the preheated oven for 60 minutes without opening the oven door. Turn off oven and leave cheesecake inside with door closed for 60 minutes more, allowing residual heat to set the cheesecake. Open oven door slightly at 1 hour and leave cheesecake in the cooling oven for another 30 minutes. Remove cheesecake from oven and let cool at room temperature for 60 minutes more.
Refrigerate cheesecake for 1 hour. Unhook the clasp on springform tin and slowly remove ring, making sure not to touch the sides of the cake. Place cheesecake in the freezer, covered or uncovered, 8 hours to overnight. Remove from freezer 1 hour before serving.
Prepare the topping just before serving: Place honey in a microwave-safe bowl and heat slightly. Stir in whisky. Arrange remaining 75g hazelnuts around edge and in the centre of cheesecake. Drizzle honey-whisky mixture on top.