In a large microwave-safe bowl, combine semi-sweet chocolate, peanut butter, and butter. Microwave in 30-second intervals for about 1-2 minutes, stirring well between bursts until the mixture is completely melted and smooth.

After the chocolate mixture is smooth, add in the vanilla extract and a pinch of salt, stirring to incorporate. Carefully fold in the Rice Chex cereal until fully coated.

Transfer the mixture into a large paper grocery bag or mixing bowl, add powdered sugar, seal the bag or cover the bowl, then shake vigorously for a minute until every piece is dusted.

Line baking sheets with parchment paper, spread the coated mixture in clumps, and let it sit at room temperature for 15-20 minutes, or freeze for 10 minutes for firmer clusters.

Once set, break into pieces for serving. Enjoy chilled from the freezer for an extra satisfying crunch.