Preheat your broiler and arrange marshmallows in a single even layer on a parchment-lined baking sheet. Toast marshmallows until they've browned to your preference. Watch them closely as they can go from nicely browned to black and burnt really quickly. Remove marshmallows from the oven and allow to cool for 5 minutes.

Once cooled, use a spatula to scrape the marshmallows into a food processor. Add the sweetened condensed milk and pulse until mixture is smooth and most of the marshmallow has broken up. This can also be done in a blender.

In the bowl* of a stand mixer fitted with the whisk attachment, whip the cream until soft peaks form. Add the marshmallow mixture and finish mixing by hand until fully incorporated. Place in the freezer while you prepare the pan for the ice cream sandwiches.

Line a 9x13 inch rectangular dish with plastic wrap, leaving a good amount of overhang on the sides. Break the graham crackers in half and arrange them on the bottom of the pan. To solve the issue of extra space on the side, use a ruler as a "receding wall" underneath the plastic wrap along with a freezer-safe item that'll fit behind it. I used two regular-sized Butterfinger chocolate bars. See picture above.

Pour ice cream mixture evenly over graham crackers and arrange the remaining graham crackers on top. Wrap the plastic wrap over the ice cream sandwiches and freeze for at least 4 hours, preferably overnight.

Once ice cream sandwiches have frozen, remove from the pan and unwrap the plastic wrap. Using a sharp, warm knife, cut the sandwiches along the graham cracker edges, making 15 squares and 5 small rectangles. Place sandwiches on a wax paper-lined baking sheet and return to the freezer to firm up for 20 minutes.

Prepare a second baking sheet by lining it with wax paper. Heat the chocolate in a bowl in the microwave until melted and smooth, about 1 to 2 minutes. Place the crushed Butterfinger in a separate bowl. Working quickly in batches of 3-4, dip sandwiches halfway into chocolate, then into the crushed Butterfinger, and onto the second baking sheet in the freezer. Once the chocolate has set, ice cream sandwiches can be individually-wrapped in plastic wrap and stored in the freezer for up to 2 months.