In a large mixing bowl, beat together butter, peanut butter, granulated sugar, and brown sugar until smooth and creamy.
Add wet ingredients
Mix in the egg, vanilla extract, and milk until well combined.
Incorporate dry ingredients
Gradually add the flour, baking soda, and salt, mixing until a soft dough forms.
Shape the cookies
Roll the dough into 1-inch balls and coat them in granulated sugar. Place them on a baking sheet lined with parchment paper, spacing them about 2 inches apart.
Bake
Preheat your oven to 375°F (190°C) and bake for about 8-10 minutes, or until the edges are slightly golden.
Add chocolate
Immediately after removing from the oven, gently press a chocolate kiss into the center of each cookie. The heat will slightly melt the chocolate, securing it in place.
Cool
Transfer cookies to a cooling rack and let them set before serving.