Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a bowl, whisk together flour, baking soda, and salt.
In another bowl, cream butter, peanut butter, granulated sugar, and brown sugar until fluffy.
Add egg, vanilla extract, and milk, then mix until combined.
Gradually add dry ingredients into the wet mixture and mix until a soft dough forms.
Roll dough into 1-inch balls and coat each ball in granulated sugar.
Place on baking sheet 2 inches apart.
Bake for 8–10 minutes until edges are lightly golden.
Remove from oven and immediately press a Hershey Kiss into the center of each cookie.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.
