In a food processor, pulse the cereal until finely crushed. Add butter and pulse until well combined and when you pinch the mixture together, it holds well.
Divide crust evenly and press the mixture into the bottom of each mini mason jar. Refrigerate until ready to fill.
In a stand mixer fitted with a paddle attachment or with a hand mixer, beat the cream cheese and peanut butter until smooth, about 2 minutes.
Add the remaining ingredients and keep mixing it for another minute or so or until you have a smooth batter. Divide the batter among the mini mason cars, cover and refrigerate for 4 hours or overnight.
When ready to serve, top with a spoonful of marshmallow fluff and serve immediately!
Storage: You can store these in the refrigerator, covered, for up to 5 days. You can also freeze them for longer storage - about two months. Make sure to cover them well to prevent freezer burn. Mark them with the date, and thaw in the refrigerator before serving.Softening the Cream Cheese: Softening the cream cheese might seem like an unnecessary step, but it really goes a long way toward keeping the batter smooth and lump-free.Add Chocolate: If you like, you can add chocolate to the recipe by garnishing the cheesecakes with shaved chocolate or a chocolate drizzle.Add Nutella: For a Nutella twist, make half of the batter with peanut butter, and half with Nutella! Yum.Add Crunch: Feel free to sprinkle a layer of chopped peanuts over the tops of the cheesecakes for even more added crunch.