Preheat oven to 375℉. Line a cookie sheet with parchment paper or spray the sheet with vegetable spray.
Sift together flour, baking soda and salt; set aside.
Using an electric mixer, cream together butter, peanut butter, granulated sugar, and brown sugar.
Add egg, milk, and vanilla; beat until well blended.
Gradually add flour mixture, mixing thoroughly. If the dough is very soft, refrigerate for about 1 hour.
Form dough into 1-inch balls. *** see notes.
Roll cookies in sugar and place 2 inches apart on the cookie sheet.
Bake until very light brown and puffed, for about 9-to 11 minutes.
Remove sheet from oven and lightly press a candy kiss into center of each cookie, allowing it to crack slightly. Cool for 2 minutes.
The chocolate will bond to the cookie as the cooke. Remove the cookies to a wire rack and cool completely and store in an airtight container.