Before anything else, unwrap all the chocolate kisses and set them in a bowl. Heat the oven to 375°F (190°C).

In a large bowl, beat the butter, peanut butter, 1/3 cup granulated sugar and the brown sugar until light and creamy. Beat in the egg, milk and vanilla until smooth.

In a separate bowl, whisk together the flour, baking soda and salt. Stir into the peanut butter mixture until a soft dough forms.

Roll the dough into 1-inch balls. Roll each ball in granulated sugar and place 2 inches apart on ungreased baking sheets.

Bake 8–10 minutes, until the cookies are puffed and very lightly golden at the edges. Do not let them brown — they should stay soft.

The second the pan comes out of the oven, press one chocolate kiss firmly into the center of each cookie. The cookie will crack a little around the edges — that's exactly right.

Move the cookies to a wire rack and let them cool completely, until the chocolate is set firm again, before stacking or storing.