Preheat oven to 160°C. Line base and sides of a 20cm (base measurement) springform pan with baking paper.
Process biscuits in a food processor until finely crushed. Add melted butter. Process until well combined. Spoon into the prepared pan and use a straight-sided glass to spread and press over base and side. Place in the fridge for 30 mins to chill.
Meanwhile, place half the condensed milk in a small saucepan. Add golden syrup, half the salt, 10g chopped butter and 2 tbs water. Place over medium heat. Cook, stirring, for 7-8 mins or until mixture is golden and thickens slightly.
Process the cream cheese in a clean food processor until smooth. Add the sugar and vanilla. Process until smooth. Add the eggs. Process until smooth. Pour into the lined pan. Spoon over the condensed milk mixture and gently marble. Place on a baking tray and bake for 45 mins or until almost set in the centre. Turn oven off. Leave the cake in the oven, with the door ajar, for 1 hour to cool completely. Place in the fridge to chill.
Place extra sugar and 2 tbs water in a small saucepan over low heat. Cook, stirring, for 5 mins or until the sugar dissolves. Increase heat to high. Bring to the boil. Cook, without stirring, for 5-7 mins or until golden. Remove from heat. Whisk in the remaining condensed milk and chopped butter until smooth and combined. Cool slightly.
Top the cheesecake with a dollop of cream and drizzle with caramel. Sprinkle with the remaining salt. Serve with the remaining cream and caramel.