Step 1 In the bowl of a stand mixer fitted with the paddle attachment, beat 12 ounces peanut butter and the butter until smooth. Add the powdered sugar and beat until smooth.
Step 2 Crush the crisped rice cereal to a coarse meal: Pulse the cereal in batches using a food processor, or place the cereal in a large sealable plastic bag and crush using a rolling pin.
Step 3Add the cereal to the peanut butter mixture and beat to combine. Press the mixture into a greased 13- by 9-inch baking dish. Chill until firm.
Step 4Place 2 cups chocolate chips in a glass measuring cup or dish and microwave, stirring every 30 seconds or so, until melted and smooth. Stir in the remaining 1/3 cup peanut butter until fully combined and smooth. Spread the melted chocolate mixture over the peanut butter bars. Sprinkle over the peanuts. Melt the remaining ½ cup chocolate chips, then drizzle the melted chocolate over the peanuts. Chill until the chocolate is firm, then cut into bars.