Prepare the Pistachios: Pulse the pistachios in a food processor until they are finely ground but not completely powdered.
Melt the Peanut Butter and Chocolate: In a small microwave-safe bowl, melt the peanut butter and white chocolate chips together. Heat in 20-second increments and stir until smooth.
Mix in the Sweetener: Add powdered erythritol (or your preferred keto sweetener) to the melted mixture. Stir well to combine.
Coat the Puffed Rice: In a large mixing bowl, add the puffed rice and coconut flakes (if using). Pour the melted mixture over the puffed rice, stirring until it’s evenly coated.
Add the Ground Pistachios: Sprinkle the ground pistachios over the coated rice mixture. Gently toss everything together, ensuring the pistachios coat each piece of the puffed rice.
Let it Set: Spread the mixture in a single layer on a parchment-lined baking sheet. Allow it to cool for about 30 minutes so it firms up.
Serve: Once cooled, break the mixture into pieces and store in an airtight container.