Whisk together flour, baking soda, and salt in a bowl; set aside.
Beat butter and peanut butter in a large bowl using an electric mixer until creamy.
Mix in brown sugar and ¼ cup of granulated sugar until smooth.
Beat in egg, vanilla extract, and milk until combined.
Add dry ingredients and mix just until soft dough forms.
Scoop tablespoon-sized dough balls onto a sheet and chill for 15 to 20 minutes.
Preheat oven to 350°F and line baking sheets with parchment paper.
Roll chilled dough into balls, coat each in remaining granulated sugar, and place 2 inches apart on prepared sheets.
Bake for 8 to 10 minutes until tops crack and edges appear set without browning.
Cool cookies 5 minutes, then press a Hershey’s Kiss into the center of each.
Let cookies sit 5 to 10 minutes more, then transfer to a rack to cool completely.