1) Preheat the oven to 180C/Gas 4.
2) Place the digestive biscuits, 60g of the walnuts and brown sugar in a food processor and process until finely ground. With the motor running, add the butter through the feed tube and process until the mixture just comes together.
3) Spray the bottom and sides of a 23-cm springform tin with cooking spray. Pat the mixture evenly into the bottom of the tin, place on a baking sheet and bake in the oven until lightly golden brown and just set, about 8 minutes. Remove to a baking rack and let cool completely.
4) Combine 50g of the caster sugar and the orange zest in a food processor and process until combined.
5) Place the cream cheese in the bowl of a stand mixer fitted with the paddle attachment and beat until light and fluffy, 3 to 4 minutes. Add the orange sugar, remaining caster sugar and the light muscovado sugar and beat again until the sugar is incorporated and the mixture is light and fluffy.
6) Add the eggs one at a time and mix until just incorporated, scraping the sides and bottom of the bowl. Add the vanilla seeds and vanilla essence and beat until combined. Add the salt and double cream and mix until just combined.
7) Scrape the mixture into the prepared shell. Set the cheesecake tin on a large piece of heavy-duty aluminium foil and fold up the sides around it. Place the cake tin in a large roasting tray. Pour hot tap water into the roasting tray until the water is about halfway up the sides of the cheesecake tin; the foil will keep the water from seeping into the cheesecake. Bake until the sides of the cake are slightly puffed and set and the centre still jiggles, about 55 minutes.
8) Turn the heat off and prop the oven door open with a wooden spoon and allow the cake to cook in the water bath for 1 hour. Remove the cake to a baking rack and allow to cool to room temperature for 2 hours. Cover the cake and refrigerate for at least 4 hours and up to 24 hours until chilled through.
9) Top with the warm apple topping, drizzle liberally with the caramel sauce and sprinkle with the remaining toasted walnuts. Serve additional sauce on the side.
For the apple mixture:
1) Bring the apple juice, sugar and vanilla pod to a boil in a large saute pan over high heat and cook until slightly thickened and reduced to 120ml.
2) Stir in the butter until melted. Add the apples and cook, stirring occasionally, until lightly caramelised and soft. Add the apple brandy and cook until reduced by half. Transfer the apples to a plate and let cool slightly.
For the apple-caramel sauce:
1) Place the caster sugar and water in a medium saucepan and bring to a boil over high heat, without stirring, swirling the pot occasionally to even out the colour, until amber in colour, 10 to 12 minutes.
2) While the caramel is cooking, place the double cream in a small pan and bring to a simmer over medium heat. Remove from the heat and keep warm.
3) When the caramel has reached the desired colour, slowly whisk in the double cream and salt and whisk until smooth. Remove from the heat and stir in the apple brandy and vanilla essence. Keep warm.