Line a 9 by 5-inch loaf pan with plastic wrap, leaving overhangs on all sides.
Whisk the pudding mix and milk together for 2 minutes and let sit for 5 minutes.
Beat the cream until stiff peaks form. Fold in the marshmallow fluff until fully incorporated. Place about ½ cup of the mixture in a covered bowl and refrigerate until later.
Line the bottom of the pan with S’morables, breaking them up if needed to fit snuggly. Top with half the pudding, then half the rest of the cream mixture. Top with another layer of S’morables then repeat the layers. Top with another layer of S’morables, cover with plastic wrap and refrigerate for at least 8 hours.
Remove the plastic wrap from the top of the cake, invert onto a platter, remove and discard the rest of the plastic wrap. Top with the reserved cream mixture and place the marshmallows on top. Torch the marshmallows with a kitchen torch and serve.
If you do not have a kitchen torch, place the marshmallows on a parchment lined baking sheet and place under the broiler until they have browned but have not started to melt. When cool, place on top of the cake. Do not try to put the whole cake under the broiler, as it will melt the cream.