Combine graham cracker crumbs and melted butter. Spread out on a sheet pan and toast in the oven for 10 minutes. Let cool.
Place mini marshmallows in a single layer on a sheet pan and toast under the broiler for about 2 minutes till browned. Alternately, use a kitchen torch to lightly char mini marshmallows.
With an electric mixer, beat heavy cream to soft peaks. Use a spoon or spatula to fold in the sweetened condensed milk and then the marshmallow cream. Be careful not to stir and deflate the whipped cream. It's okay if some streaks of marshmallow cream remain.
Fold the chopped chocolate carefully into the marshmallow whipped cream mixture.
Layer the marshmallow whipped cream, graham cracker crumbs, and toasted marshmallows into a 9x5-inch loaf pan or bowl.