Spread 1 cup of fudge on top of the pretzel crust. Freeze for an additional 15 minutes (this freezing helps the ice cream spread easier).

Remove chocolate ice cream from the freezer about 10 minutes before adding it to the cake. Spread the chocolate ice cream on top of the first fudge layer. Freeze for 30 minutes to 1 hour.

Spread 1 cup of fudge on top of the chocolate ice cream. If the ice cream didn't freeze through enough, it may start melting as you add the fudge and come through during the spreading. That's ok, just work around it or continue spreading (but this is why the additional freeze is recommended after each layer). Place in the freezer for 15 minutes while preparing the next layer.

Remove the vanilla ice cream from the freezer for 10 minutes to soften slightly. Stir in the chopped peanut butter cups until thoroughly combined. Spread on top of the fudge layer and return to the freezer for "the big freeze". Freeze for at least 4 hours, or overnight (preferred).

Before serving, spread the final 1 cup of fudge on top of the cake. Top with additional peanut butter cups and/or pretzels as desired. Freeze again for 30 minutes if you want the fudge to be more firm, or serve immediately. Drizzle with salted caramel if desired.