Line an 8x8-inch pan with two strips of wax or parchment paper: the strips should be as wide as the bottom of the pan and be long enough to extend over the edges; have one strip go in one direction and criss-cross the other over it. This will allow you to lift the fudge out of the pan once it's set.
Have a small bowl of ice water ready next to the stove.
Prepare the potato chips:
Place the 1¼ cups of chips into a small bowl, and use a potato masher or the bottom of a glass to crush them into coarse pieces. Hold these aside.
Cook the fudge mixture:
Combine the sugar, Marshmallow Fluff, evaporated milk, butter, vanilla, cinnamon, and cayenne in a large saucepan over medium-low heat. Stir the mixture frequently until everything melts and is smooth.
Increase the heat slightly to medium, and stirconstantly scraping the bottom of the pan until the mixture comes to a rolling boil. (Note: this stuff is hot - I mean like molten lava-hot, so be very careful not to get splattered.)
Continue stirring the mixture constantly for another 3 minutes until it reaches the "soft ball" stage: use a spoon to drizzle a tint bit into the ice water - the fudge mixture is ready when you can form it into a soft ball in the water. If it's not ready cook it for 30 seconds to a minute longer and test again.
Remove the pan from the heat.
Stir in the peanut butter until it is thoroughly combined and the mixture looks smooth.
Pour into the pan:
Immediately pour the peanut butter fudge mixture into the prepared pan and spread it into an even layer.
Pour the crushed potato chips over the top. Use a spoon to stir through a few times to incorpoate the chips into the fudge mixture. Add a few whole chips (or larger pieces) across the top.
Place the pan on a wire rack and leave it out at room temperature to cool and set, which should take about two hours.
Slice the fudge:
Once the fudge is set, use a sharp knife to slice the fudge into 36 pieces. (Or larger pieces, if you'd rather!)
Notes
Tip:
Store the fudge wrapped at room temperature for up to 4 days.