In a microwave-safe bowl, combine semisweet chocolate chips, white chocolate chips, and butter. Heat in 30-second bursts, stirring after each, until melted and smooth (about 1-2 minutes). Mix in peppermint extract.

In a large mixing bowl, carefully pour in the Rice Chex cereal. Gently fold in the melted chocolate mixture until each piece is coated.

Sprinkle crushed peppermint candies and a pinch of salt over the mixture. Mix gently until combined.

Transfer the mixture into a gallon-size zip-top bag. Add powdered sugar, seal tightly, and shake vigorously for 30 seconds.

Spread the mixture onto a parchment-lined baking sheet and let it cool for 15 minutes. Break into pieces and serve.