Place the brownie mix in a microwave-safe bowl and heat in 30-second increments, stirring well between each heating, for 3-5 minutes or until the mixture reaches 165 degrees Fahrenheit with a digital thermometer.

Set the heat-treated brownie mix aside.

In a second, large microwave-safe bowl, combine the chocolate chips, peanut butter, and salted butter and heat for 60 seconds.

Stir the mixture well and continue heating in 15-second increments, if needed, until it is smooth and fully melted.

Add the vanilla and stir well.

Gently fold in the Rice Chex, careful not to crush them, until completely coated with the chocolate mixture.

Place 1/3 of the brownie mixture in a large, sealable plastic bag, then put half of the Chex mixture into the bag.

Repeat by pouring the remaining brownie mix on top of the mixture and seal the bag.

Shake the bag well until the Chex mixture is evenly coated with the brownie mixture.

Spread the coated Chex mixture on a large sheet of aluminum foil or parchment paper and let cool completely before serving.