Melt the chocolate chips and peanut butter together in a large microwave-safe bowl. Heat in 30-second bursts, stirring between each until smooth.

Once melted, stir in the vanilla extract if using.

Pour the Rice Chex into the bowl with the melted mixture and gently fold until coated.

Transfer the mixture into a large resealable plastic bag, add the powdered sugar, and shake until evenly coated.

Pour the cereal back into a bowl and add the crushed Butterfinger bars. Gently mix until evenly distributed.

Let the mixture sit for about 30 minutes to allow it to set.