Melt the butter in a small bowl in the microwave for 1 minute/2 minutes. – Be sure to keep an eye on it as it can turn really quickly! If you don’t have a microwave, melt gently in a small saucepan on low.
In a separate bowl, place the brown sugar and the crushed biscuits.
Begin to gradually stir in the butter until it gains a consistency similar to wet sand.
Line a cake tin with greaseproof paper, and spoon the biscuit base mixture into the tin, smoothing out so it covers the whole of the tin.
Chill for 30 minutes.
Whilst the biscuit base is chilling, beat together the cream cheese, vanilla extract and caster sugar in a bowl, gradually folding in the double cream. It should be of a thick, dropping consistency in nature.
Once the biscuit base has chilled, spoon over the filling, and smooth out with a knife.
Leave to chill in the fridge for a further two hours and serve.