Preheat oven to 350 °F (177 °C) and line a large baking sheet with parchment paper or silicone baking mats.
In a large bowl, whisk together flour, baking soda, and salt.
In the bowl of a stand mixer fitted with the paddle attachment, cream together butter, peanut butter, and sugars until light and fluffy, about 2 minutes.
Add the egg, milk, and vanilla extract and beat until incorporated.
Carefully add the dry ingredients until cookie dough forms.
Pour 1/2 cup granulated sugar in a small bowl.
Using a medium cookie scoop, scoop dough and roll into a ball. Then roll in sugar and place on prepared baking sheet. Repeat until all cookie dough has been used up.
Bake for 8-10 minutes then remove from oven and immediately place a Hershey kiss in the center of the cookie. Let cool for 15-20 minutes then carefully move cookies to a wire cooling rack to cool completely.