Sift together flour, baking soda and salt; set aside. Using an electric mixer, cream together butter, peanut butter, 1/2 cup granulated sugar and light 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.
Preheat oven to 375 degrees. Spray, oil or line a cookie sheet with nonstick liner and set aside. Roll dough into 1-inch balls. (For a precise number of cookies, divide the dough into 5 pieces, and shape each piece into 12 balls.)
Roll cookies in sugar and place 2 inches apart on cookie sheet. Bake until very light brown and puffed, 6 to 8 minutes. Remove sheet from oven and lightly press a candy kiss into center of each cookie, allowing it to crack slightly. Return to oven until light golden brown, 2 to 3 minutes. Remove from oven, cool completely and store in an airtight container.
