In a food processor, blitz the biscuits / cookies to crumbs. Mix with the melted butter. Oil the sides and base of a rectangular tart tin with a removable base, then press your cookie mixture into the bottom until firm. Place in the fridge to set.
For the whipped nougat
Place the sugar, glucose, water and salt in a medium saucepan. Stir over low-medium heat until the sugar dissolves. Place a lid on and let the mixture cook without touching it for 7 minutes.
Remove the lid and continue to cook the syrup until it reaches 270F on a sugar thermometer.
Start whipping the egg whites in a stand mixer until they reach stiff peaks.
With the mixer on low, start to very slowly pour the syrup into the egg whites. This should be a very slow, steady stream that should take at least 2 minutes to fully add.
Turn the mixer up to medium and beat for around 10 minutes until it looks very thick and glossy. The nougat will be very sticky at this stage but still look quite runny.
Add the melted chocolate and malted milk powder and beat until just mixed through.
This next part is easiest with your hands (sorry), just make sure to dampen your hands first. Scrape the nougat into your tart case. Re-dampen your hands (just damp, not dripping wet), then press the nougat out over the cookie base evenly.
Place in the fridge to set.
Melt the chocolate in a bowl in the microwave, in 30 second increments. Stir well between each and only do this until it is just melted and smooth. This should take no longer than 2 minutes. Pour the chocolate over the top of your nougat and use an offset spatula to smooth
If you don't want to make your nougat from scratch, you can use a jar off Marshmallow Fluff, then beat in the melted chocolate and malt powder