Puppy Chow Party Mix

Place cereal in a large bowl. Heat chocolate, peanut butter, butter, and salt in a medium heatproof bowl set over a saucepan of barely simmering water (do not let bowl touch water), stirring, until chocolate is melted and mixture is smooth. Remove from heat and stir in vanilla. Pour chocolate mixture over cereal and toss with 2 spoons or spatulas until coated. Let cool slightly, about 10 minutes.

Transfer cereal mixture to a large clean bowl (so powdered sugar doesn’t absorb into chocolate coating from original bowl). Sift ½ cup powdered sugar through a fine-mesh sieve onto cereal, coating entire surface. Toss to coat. Repeat 2 more times.

Transfer cereal mixture to 2 parchment-lined sheet trays, spreading evenly. Sift ½ cup powdered sugar over both trays (do not mix). Chill 2 hours or let sit at room temperature overnight (break into individual pieces, but leave some clumps, if sitting out overnight).

Transfer cereal mixture and powdered sugar from sheet trays to a large clean bowl and toss to coat. Sift remaining ½ cup powdered sugar over and toss to coat again. Add M&M’s, peanuts, and pretzels; toss to combine.

Do Ahead: Puppy chow can be made 2 days ahead. Store in an airtight container at room-temperature.