Drop the biscuits into a food processor and process until they reach fine crumbs.
With the mixer still running add the cooled melted butter and salt and mix until the mixture resembles wet sand.
Tip the biscuit crumbs into an 20cm (8 inch) round x 7cm (2.5 inches) deep springform cake tin.
Use the base of a glass to press the crumbs into an even layer at the base of the cake tin and up the sides. The pie crust should be about 3cm (1 inch) deep. Place in the freezer for 30 minutes to set (or in the fridge for 1 hour).
Meanwhile, to make the cheesecake filling, place the cream cheese, sour cream, icing sugar and vanilla into a large bowl. Beat the mixture until smooth and creamy.
In a separate bowl, whip 200g of the double cream (the rest is needed for the topping) until it is thick and at the soft peak stage, then gently fold it into the cream cheese mixture until fully incorporated.
Remove the set biscuit base from the freezer (or fridge).
Ensure that the base is firm, and the sides are well-formed and then pour in the cheesecake filling, smoothing the top to a nice finish.
If your Sticky Toffee Sauce has been chilled it will be very thick. Pour into a warm saucepan and whisk to smooth to a pourable consistency (but don’t heat it) Pour the sticky toffee sauce over the top of the cheesecake filling. Smooth and swirl it over the top, being careful not to disturb the filling underneath. Then cover and chill the cheesecake in the fridge overnight to set.
Pour the remaining 300g double cream into a large mixing bowl and whip to the soft peak stage. Spoon at the edges of the cheesecake.
Smash the extra 30g biscuits to create fine crumbs then sprinkle over the top of the whipped cream edge.