Crush biscuits in a food processor to a fine crumb. Transfer to a medium-sized bowl and mix in the butter. Press evenly into a 20cm springform cake tin and refrigerate for 30- 45 minutes until set firm.
Warm the peanut butter slightly in a microwave until just softened.
Beat cream cheese and sugar with an electric mixer until smooth. Gradually beat in gelatin mixture, vanilla extract and peanut butter until combined. Fold in thickened cream. Spoon over the chilled biscuit base, and using a spatula, smooth down the top evenly.
Refrigerate for 4 ½ hours or overnight.
For the brittle; spread the peanuts out on one layer on a flat baking tray lined with baking paper and set aside.
Heat the sugar with ½ cup water in a medium saucepan over high heat. Stir with a metal spoon until the sugar has dissolved then stop stirring and cook for 8-10 minutes until golden brown. Remove from heat and stir the butter through until well combined.
Pour hot caramel over the peanuts, sprinkle with sea salt and allow to cool on a cold surface for 15 minutes until set hard. Break into shards.
To make the caramel sauce; melt the butter over low heat in a pan. Add the brown sugar and mix until dissolved. Add the milk and stir until smooth. If the caramel is too thick add a teaspoon more milk. Allow to cool.
To decorate, top the cheesecake with caramel shards, caramel popcorn and drizzle with caramel sauce.