Preheat oven to 350 °F (177 °C) and line baking sheets with parchment paper or silicone baking mats.
In the bowl of a stand mixer (or a large bowl with a hand mixer), cream together butter and sugar until light and fluffy. Add the egg and vanilla extract and beat until incorporated.
In a medium bowl, whisk together flour, baking soda, and salt.
Add flour mixture, alternately, with milk, to the butter mixture and mix until fully incorporated. Finally, add the sugar crystals to the dough.
Using a medium cookie scoop (or 1 1/2 tbsp of dough), place cookie dough on baking sheets.
Bake cookies for 12-13 minutes, or until edges are turning slightly brown and crisp. Remove from oven and immediately after 2 minutes, press Hershey Kiss into the center of the dough. Do NOT touch it anymore at this point.
After 5 minutes, gently transfer the cookies to a wire cooling rack to cool completely.