Heat oven to 375 degrees F. Line several baking sheets with parchment paper and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter, peanut butter, and sugar for 2 minutes on medium speed. Turn mixer to low and add in egg, milk, vanilla, and red food coloring. Mix for about 30 seconds to incorporate, then turn mixer to medium-high and blend until light and fluffy, scraping down the sides of the bowl, as needed.
In a separate bowl, whisk together the cocoa, flour, baking soda and salt. With mixer on slow, add flour mixture to sugar mixture and beat until just combined.
Shape dough into 1 inch balls. Pour red sanding sugar onto small plate or bowl. Roll dough ball in red sanding sugar and place on prepared cookie sheet about 2 inches apart. Bake for 8 to 10 minutes.
Once cookies are done baking, remove from oven and immediately press a chocolate Kiss into the center of each cookie. The cookie should crack around edges.
Allow cookies to cool completely before removing from baking sheets.