Measure cereal in bowl: Pour cereal into a very large mixing bowl, set aside.: The cereal should sound lively as you pour it into a very large mixing bowl, a crisp rustle that signals freshness; the goal is room to move so each piece can be evenly coated later. I like using my largest bowl so the cereal can be tossed without spilling. If you skimp on bowl size you will struggle to coat without crushing the pieces, which results in a denser final snack.
Melt chocolate chips with butters: To a medium mixing bowl add chocolate chips, peanut butter and butter. Heat in microwave at 50% power for 30 seconds. Stir.: The initial melt will smell like warm cocoa with a faint buttery aroma, and the chips will become glossy as they begin to soften; use a medium mixing bowl and heat at 50% power for 30 seconds, then stir to encourage even melting. Stirring distributes heat and prevents hot spots that burn the chocolate. A common mistake is rushing with high microwave power, which can scorch the chocolate and create grainy texture, so be patient and stir frequently.
Continue heating until melted and smooth: Return to microwave and heat at 50% power for 20 seconds, stir. Repeat until chocolate has been melted. Stir in vanilla.: As you return the bowl to the microwave in 20 second bursts at 50% power, listen for a gentle hiss and watch the mixture become uniformly glossy; stop heating when there are just small unmelted streaks and finish stirring until smooth, then blend in the vanilla extract . The smoothness indicates proper emulsion of butter and chocolate with peanut butter . If the mixture becomes lumpy, it likely overheated, and you can rescue it by stirring in a small extra pat of butter or a teaspoon of oil off heat to restore gloss.
Toss chocolate mixture with cereal: Pour mixture over cereal and gently toss with a rubber spatula to evenly coat (mixture may be thick, it may take a few minutes to toss).: When you pour the warm chocolate into the bowl of rice chex cereal you will immediately notice the scent of chocolate spreading through the air; use a rubber spatula to fold and gently coat, working patiently since the mixture can be thick and resist movement. The tactile feedback is important, you should see each piece take on a sheen but remain separate. If you try to rush and slam the cereal, you risk breaking pieces and creating dust, so take a few minutes and gently fold until coverage is even.
Toss coated cereal with powdered sugar: Pour in powdered sugar and gently toss to evenly coat. Alternately you can pour mixture into a gallon size resealable bag, pour in powdered sugar, seal bag and shake to evenly coat.: The final step produces a satisfying soft, dry patina as you add powdered sugar and toss; either toss gently in your bowl until each piece looks evenly dusted, or transfer the coated cereal into a gallon size resealable bag, add the sugar, seal, and shake briefly until uniform. The powdered sugar creates a barrier that prevents clumping and gives the classic look. Over shaking in a small container can pulverize pieces, so use a roomy bag or work carefully by hand to avoid crushing the cereal.