Line the base and sides of a 22cm cake tin with greaseproof paper- use oil as butter will chill too much and make removing the pie difficult.
Make the crust: Using a food processor blitz the digestives into fine crumbs.
Melt the snickers and butter together in a saucepan set over a medium heat then tip into the digestives and blitz to combine well. Press into the cake tin, and push down evenly with the back of a spoon until the bottom and sides are completely covered and come right the way up to the top of the tin. Set aside to chill in the fridge.
For the caramel and peanut layer: Melt the snickers bars in a bowl set over a pan of simmering water until fully melted then stir in the salted peanuts. Pour into the cake tin and spread out to cover the base evenly.
Make the chocolate layer: In a medium pan add the cream and heat until nearly boiling. Remove from the heat and add the milk and dark chocolate, stirring until everything has melted together and has a smooth, silky consistency. Set aside to cool a little then pour over the caramel mixture- it will come right up to the top. Leave to set for a minimum of 4 hours, ideally overnight.
To serve: Remove the pie from the tin and transfer onto a serving plate. Whip the double cream, icing sugar and vanilla together to soft peaks. Chop the snickers and sprinkle over the top, then drizzle with caramel sauce and sprinkle over the peanuts.