Put chocolate pudding mix in a large bowl, add the milk and whisk until light and creamy. Set aside for 5 minutes - it should thicken to a pudding consistency. (Check the package directions in case your pudding mix requires boiling)
Pour the cream into a second bowl and whip to soft (not stiff) peaks. Take care not to over-whip as double cream has a high fat content and can easily turn buttery. You are now ready to assemble your trifle.
Crush 450g (16 oz / 40 cookies) of the Oreos to a crumb (this is most easily done in a food processor) and leave 350g (12 oz / 30 cookies) whole.
First, spoon in one third of the chocolate pudding.
Follow with half of the crushed Oreos. (I crush them with a food processor as it's quick, but you can pop them in a ziplock bag and bash with a rolling pin if you prefer)
Next, pile in one third of the whipped cream.
Top with a layer of Oreos, laying flat.
Now spoon in another third of the chocolate pudding (half of what’s remaining).
Now add another layer of crushed Oreos, using all but a couple of large handfuls (about 100g/3.5oz/9 cookies).
Now spoon in another third of the whipped cream (half of what’s remaining).
Top with another layer of Oreos, laying flat.
Fold all but a couple of spoonfuls of crushed Oreos into the remaining whipped cream, then pile onto the top of the trifle the should take you just above the rim of the bowl.
Push the remaining Oreos onto the top, standing up in a circle.
Finish by sprinkling on the last of the Oreo crumbs.
Video
Notes
Vanilla flavour pudding mix would also work for this recipe and give a nice colour contrast.