Usually requires a menage-a-trois involving one man and two women. One woman performs oral sex while the other performs a rimjob(please see definition of rimjob if you are unfamiliar with the term) At the height of clmax, the male ejaculates copious amounts of semen into the fellating woman's mouth while simultaneously taking a dump in the mouth of the woman giving him the rimjob. Both women then hold their respective treasures in their mouth, face each other, and engage in a deep, passionate french kiss. This mixes the shit and the semen in both their mouths resulting in "milk and cookies"
*Note-this can be performed on one woman or one man, however it takes a lot of patience and practice. One either has to hold a mouthful of semen while taking a mouthful of shit or vice versa. It should also be noted that it IS possible to make one's self a milk and cookies, but eating your own is just yucky.
John invited the old widower from next door over last night, and we talked her into sharing John's milk and cookies