Begin by lining your 9x13-inch baking dish with parchment paper. This ensures easy removal of the treats once they're set.
In a microwave-safe bowl, combine the semisweet chocolate chips, creamy peanut butter, and salted butter. Microwave in 30-second intervals, stirring in between, until everything is completely melted and smooth. This should take about 1 to 2 minutes total.
Once the mixture is smooth, stir in the vanilla extract until fully incorporated.
In a large mixing bowl, combine the miniature marshmallows and Rice Chex cereal. Pour the melted chocolate mixture over the cereal and marshmallows, and gently fold everything together until all the Rice Chex are evenly coated.
Spoon the mixture into your prepared baking dish. Use the rubber spatula to spread it out evenly and press it down gently to compact it.
Allow the mixture to cool at room temperature for about 30 minutes or until it is firm enough to cut into squares.
Once set, lift the treats out of the baking dish using the parchment paper. Dust the top generously with powdered sugar, then cut into squares or bars.
