In a food processor, crush the graham crackers into fine, even crumbs. Add the sugar and melted butter and continue pulsing until fully incorporated. Press mixture into the bottom of a 9-inch springform pan, then place in the freezer until ready to fill.

Pour cereal into a large ziploc bag, seal, and use your fists or a rolling pin to coarsely crush the cereal into smaller pieces. You don't want fine crumbs, just smaller pieces.

In a medium microwave-safe bowl, melt the milk chocolate and peanut butter in the microwave for 45-60 seconds. Remove and stir until smooth. Add crushed cereal and stir to coat. Spread the coated cereal out on a parchment-lined baking sheet. Freeze for 15 minutes to allow chocolate to harden and then break the cereal into bite-sized pieces. Set aside.

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. I usually keep the oven door open a crack so that I can keep a close eye on them. Remove marshmallows from the oven and allow to cool for at least 5 minutes.

In a well-chilled bowl of a stand mixer fitted with a paddle attachment, beat half of the ice cream (4 cups) until spreadable. Add toasted marshmallows and mix just until combined, then immediately pour mixture over prepared crust. Sprinkle half of the chocolate graham clusters evenly over toasted marshmallow ice cream, then return pan to freezer until set, about 30 minutes.

Meanwhile, scoop the second half (remaining 4 cups) of the ice cream out into a medium bowl and let sit at room temperature to soften. When soft, add the peanut butter and 1 cup of the chopped peanut butter cups and stir just until combined. Pour second layer of ice cream over graham clusters and spread into an even layer. Return pan to freezer for 30 minutes before adding the rest of the chocolate graham clusters and chopped peanut butter cups around the border of the cake. Cover with foil and place in the freezer for 6-8 hours or overnight depending on your freezer.

When ready to serve, run a hot knife around the edge of the pan and carefully remove sides. Slice and serve with additional fudge sauce, if desired.