Add the powdered sugar and peanut butter powder to the bowl of a stand mixer fitted with the whisk attachment. Mix to combine. 

Next, add the corn syrup, and with the mixer on low speed, slowly drizzle in the water. 

Turn the mixer to medium speed and beat until no lumps remain. Scrape down the sides of the bowl if needed. 

Transfer the icing to a piping bag and use it to frost your favorite cookies. Allow the icing to harden before storing.