Preheat and prepare: Heat your oven to 350°F (175°C).
Line two baking sheets with parchment paper.
Cream the fats and sugars: In a large bowl, beat the butter, peanut butter, granulated sugar, and brown sugar until light and fluffy, about 2–3 minutes. This step builds structure and keeps the cookies soft.
Add wet ingredients: Beat in the egg, vanilla, and milk until smooth and well combined. Scrape down the bowl as needed.
Whisk dry ingredients: In a separate bowl, whisk together the flour, baking soda, and salt.
Combine: Add the dry ingredients to the wet mixture and mix on low just until the flour disappears.
Do not overmix.
Shape: Scoop the dough into 1-tablespoon portions and roll into balls. Roll each ball in granulated sugar to coat.
Bake: Place the sugar-coated dough balls on the prepared sheets, spacing them about 2 inches apart. Bake for 8–10 minutes, until the tops are puffed and the edges are set but not browned.
Press in the chocolate: Remove the cookies from the oven and immediately press one chocolate kiss into the center of each cookie.
The cookie will crack slightly around the edges—that’s perfect.
Cool: Let the cookies sit on the sheet for 5 minutes, then transfer to a wire rack to cool completely. The chocolate will soften from the warmth, then firm up again as it cools.
Serve: Enjoy once the chocolate is set, or dig in while it’s still a little melty if that’s your style.