Line a 9"-x-5" loaf pan with plastic wrap, allowing overhang on all sides.
In a large bowl, whisk pudding and milk until fully combined. Let cool completely.
Make marshmallow whipped cream: In a large bowl, beat heavy cream and sugar until stiff peaks form. Fold in crème and set aside.
To loaf pan, add 1 layer of graham crackers, breaking crackers up when necessary to completely fill bottom. Spread 1/3 chocolate pudding on top of that, then add an even layer of mini marshmallows (about 1/2 cup). Spread on 1/3 marshmallow whipped cream mixture, then repeat process 2 more times, ending on marshmallow whipped cream. Refrigerate overnight.
When ready to serve, invert cake onto flat serving platter and peel off plastic.
On a baking sheet, add 1/2 cup mini marshmallows. Using a kitchen torch or broiler, toast marshmallows until golden brown. Once cool enough to handle, place on top of cake. Serve immediately.