Step 1In 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 2Crush 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.