Preheat oven to 350°F (180°C). Line a cookie sheet with parchment paper. Slightly oil the paper with coconut oil. Set it aside.
In a mixing bowl, beat egg and sugar, then stir in runny peanut butter until a cookie dough forms. The dough should come together into a dough ball. See my picture above for visual help.
Form 12 cookie dough balls of about 1 inch. Roll each ball into brown sugar (optional) then place them onto the prepared cookie sheet leaving half a thumb of space between each.
Slightly press the ball with your hand palm to flatten the ball into a thick disc, then press the base of a Hershey's Chocolate in the center of the cookie to make a mark as wide as the base of a Hershey's Kiss chocolate.
Bake in the center rack for 10-15 minutes until golden brown on the sides.
Cool them down for 10 minutes on the cookie rack, then transfer the cookies on a cooling rack and place one Hershey's Chocolate Kiss in the center of each peanut butter cookie, where you had made a mark.