Blend the cookies until they are fine crumbs. Stir in the melted butter and blend it together again.
Press the crust into a 9 inch pie dish. (Lay 2 sheets of cling wrap into your dish to make for easy pie removal later)
In a medium-sized saucepan over medium heat, add the milk and chocolate.
Bring the mixture to a simmer and let the chocolate melt gently.
While simmering, mix the cornstarch with 4 teaspoons of water together to form a runny paste.
Whisk the cornstarch mix into the chocolate whisking constantly until the mix is thick and smooth.
Simmer on very low for about 2-3 minutes until the cornstarch is cooked out. Turn off the heat.
Whisk in the vanilla extract and salt.
Set aside to cool down. To prevent it from forming a skin on top lay cling film over the pan.
Once cooled pour the chocolate pudding into your prepared crust. Spread it out with a spatula if it has thickened up. Place the pie in the fridge to set for 1 hour.
For the Marshmallow Fluff: You can make it while the pie is setting in the fridge or you can make it up to a week in advance and store it in jars ready to use.
Spoon around ¾ of the marshmallow fluff on top of the pie. Note that the Fluff will spread so take care not to put too much on.
On low heat, carefully toast the top of the pie under the grill until toasted. Stand by the pie and keep a close eye on it as it toasts really fast and can burn.
You can serve the pie straight away for place it in the fridge for up to 3 days.