Whisk together the dry ingredients in a medium bowl: whisk together the flour, baking soda and salt; set aside.

In a stand mixer or with a hand mixer, cream together the butter, peanut butter, 1/2 cup sugar, and brown sugar until smooth. Scrape down the sides of the bowl if needed.

Add in the egg, milk and vanilla extract. Mix until combined. Add the dry ingredients and mix on low until combined. Avoid over mixing. Wrap the dough in plastic wrap and let chill in the fridge for at least 30 minutes. The dough can be chilled up to 72 hours.

Freeze the unwrapped chocolate kisses for 30 minutes before baking. This will help the chocolates to keep their shape and not melt.

Preheat oven to 350 degrees F. Line a large baking sheet with parchment paper. Roll the peanut butter cookie dough into balls, about 1 tablespoon of dough per cookie. Place the remaining 1/2 cup sugar in a small bowl. Roll the cookie dough balls in the sugar until they are coated.

Place the cookie dough balls onto the baking sheet, about 2-inches apart. Bake the cookies until they start to crack on the edges, about 8 to 9 minutes. Remove the baking sheet from the oven and lightly press a frozen chocolate kiss into the center of each cookie, allowing it to crack the cookie slightly. Return the baking sheet back to the oven and bake for an additional 2 minutes. Remove from the oven and let the cookies cool on the baking sheet for a few minutes. Transfer the cookies to a cooling rack and allow to cool until the chocolate kisses harden up a bit.