They come in a light blue box with the word "cookies" imprinted on it in dark red font. The cookies themselves resemble regular chocolate chip cookies. The recipe for them seems to be the same as a normal recipe for cookies, except for Plankton using nitroglycerin to substitute vanilla extract.
Role in episode
Plankton, disguised as a Sweetie Patrol girl, attempts to sell these cookies to Gary in an attempt to obtain the Krabby Pattysecret formula. He wants to hide them in a "secret spot" but Gary does not fall for it and moves the couch with Plankton on it outside.
Plankton is upset that his plan failed and throws the cookies on the ground, causing an explosion. It is at that moment revealed that Plankton used nitroglycerin as a substitute for vanilla extract.