Preheat oven to 375°F. LIne a baking sheet with parchment paper.
In the bowl of a stand mixer with a paddle attachment, add butter, peanut butter, and sugar. Mix for 2 minutes on medium speed. Reduce to low speed and add in egg, milk, vanilla, and red food coloring. Mix for about 30 seconds to incorporate. Then, increase the mixer speed to medium-high and blend until light and fluffy.
In a separate bowl sift cocoa, flour, baking soda, and salt. With the stand mixer on slow speed, add the flour mixture to the butter mixture and beat until just combined.
Remove the mixer bowl from the stand. Using a 1-tablespoon scoop, drop dough onto the lined baking sheet. Roll each scoop of dough into a ball.
Pour red sanding sugar onto small plate or bowl.
Roll each dough ball in red sanding sugar and place it back onto the prepared cookie sheet, leaving about 2 inches between each ball of dough. (If you prefer the cookies extra chewy, chill for 10 minutes in the freezer before baking.)
Bake for 7-8 minutes.
When the cookies are done baking, remove them from the oven and immediately press a chocolate Kiss into the center of each cookie. The cookie should crack around the edges.
Allow cookies to cool to room temperature before serving.