Add the white chocolate, peanut butter, and butter to a bowl and microwave for 30 seconds. Stir and repeat until melted.
Once melted, stir in the vanilla and pumpkin pie spice.
Add the Rice Chex to a large bowl and pour the melted chocolate / peanut butter over top. Using a spatula, gently stir the Chex until coated.
Add the powdered sugar to a large gallon sized zip top bag and add the coated Chex to the bag. Seal the bag and gently shake the bag to coat the Chex with the powdered sugar.
Spread the Chex onto a baking sheet to let cool to room temperature.
Once cooled, add the Chex to a large bowl and add the remaining ingredients. Stir to combine and serve.