Combine the chopped peanuts and rice cereal. I measured each with a measuring cup before combining.
Put the marshmallows and peanut butter in a bowl, and microwave for 2 to 3 minutes until melted. The marshmallows will puff up.
Mix the peanut butter and marshmallows together rapidly. It will deflate and become a sticky cream.
Put the peanuts and rice cereal into the bowl with the marshmallows and mix to combine. It will becoming sticky and stringy like natto, and will cool fast and start to harden, so work as quickly.
Put the mixture into a mold (I used a Tupperware container) lined with parchment paper. Press down on it hard to form into a rectangle. Cut when cooled.
Form golfball-sized balls of with any of the mixture that doesn't fit in the tin.
Optionally, coat the top of the bars with white chocolate. Warm the chocolate and cream in the microwave to melt.
Mix well, and spread evenly over the surface of the hardened cereal. Chill for about an hour in the refrigerator until set.
Cut into whatever size you like and enjoy.
In the U.S., Kellogg's Rice Krispies are the standard puffed rice cereal to use. It's hard to get in Japan, so I used puffed rice (pon-gashi) instead. I found it in the snacks corner of a 100 yen shop.
I used Skippy Creamy Peanut Butter.
Story Behind this Recipe
I used Kellogg's "Rice Krispies Squares Original Recipe" as a reference. Usually you use butter or margarine, but I used peanut butter instead. I added peanuts too, and changed the ingredients. I also added white chocolate since the rice cereal is not that sweet.
When mixing the cereal and marshmallows together, it hardens and sets very fast, so it's pretty tough work. Try putting a little butter on the spatula - that is supposed to help. It's easier to put the mixture into the mold and press down with your hands rather than with a spatula. The white chocolate is optional, but puffed rice is not that sweet, so the bars taste better with chocolate.