Line a 9x13 pan with foil and spray the foil with cooking spray. Set aside.
In a large heavy-bottomed pot over medium-low heat, melt the butter. Add the marshmallows and stir until almost completely melted.
Remove from the heat (the residual heat will continue to melt the marshmallows) and stir in the peppermint extract and salt. Add the cereal and stir a few times. Add the white chocolate chips and stir until evenly mixed.
Pour the mixture into the lined pan and smooth the top. Add the crushed peppermint candy and press into the crispy treats. Let cool for 20 minutes. Slice and serve!
