24-30peppermint bark squares(like Ghirardelli; 2 5.4 oz bags)
Prepare the pan: Spray an 8x8 pan with baking spray, line it with parchment paper, and spray the paper. Set aside. (Note 1)
Heat a large, heavy-bottomed pot over medium-low heat. Add the butter and heat until melted.
Stir in the miniature marshmallows, reserving 1 cup to fold in later. Stir until completely melted. Then stir in the peppermint extract.
Add the cereal and stir until it is evenly coated with the marshmallow mixture. Add the remaining marshmallows and chopped peppermint bark. Fold to incorporate, working quickly since the chocolate will start to melt. (Note 2)
Transfer the cereal mixture to the prepared pan. Spray hands with baking spray and press the mixture evenly into the pan. Set aside to cool and set, approx. 60 minutes.
Using the parchment paper, lift the bars out of the pan. Slice into squares. Store in an airtight container for up to 3 days.
Use an 8x8 pan for thick bars. For thinner bars, use a 9x13 pan.
Store the chopped peppermint bark in the freezer while preparing the cereal mixture. Keeping the chocolate cold will keep it from melting so quickly when added to the warm cereal mixture.
Using a silicone spoon or spatula will reduce sticking with the marshmallow mixture.