These are a hearty rendition of the familiar squares made from crispy rice cereal. The only difference between these and the recipe on the cereal box is the choice of cereal and the addition of cider vinegar, which cuts the sweetness and enhances the flavor of raisins.
Melt the butter in a large pot over medium-high heat. Add the marshmallows and stir until melted. Stir in the vinegar and remove from the heat. Stir in the cereal and chocolate chips until completely coated with the marshmallow mixture. Pack into the prepared baking pan and let cool until set, at least 30 minutes. Cut into 36 squares (a 6- by 6- grid) and serve.