Cream together the butter, peanut butter, and the sugars until creamy. Add in the egg and mix until fully incorporated.
Whisk together the flour, baking soda and salt in a medium bowl. Slowly add to the peanut butter mixture, making sure to fully incorporate before adding the next batch of the flour mixture. Add in the milk and vanilla extract and mix until fully combined. Refrigerate for one hour to overnight.
Scoop about a 1-inch scoop of the peanut butter cookie dough and roll into a ball. Roll the cookie dough ball in the additional granulated sugar, place the peanut butter cookie dough ball about 2 inches apart onto the baking sheet. Bake 8 minutes and then gently press a chocolate kiss into the center of the cookie until the sides of the cookie begin to crack. Return to the oven for 2 more minutes. Remove from the oven and allow to cool.
Notes
How to Make Ahead, Store and Freeze Peanut Butter Blossoms
To make ahead. These cookies are excellent to make ahead, especially throughout the holidays. They are some of our favorite Make Ahead Christmas Cookies. Simply prepare the peanut butter blossoms dough as instructed and store it in the refrigerator for 3 to 5 days.To store. Let the baked cookies cool completely, then place them on parchment-lined layers in an airtight container. The baked peanut butter blossoms cookies should stay fresh for up to one week.To freeze. Scoop the cookie dough as directed and place it onto a parchment-lined baking sheet. Place the baking sheet into the freezer for 30 minutes so that each cookie dough ball individually freezes. Once frozen, transfer the frozen peanut butter blossom cookie dough balls into a zip-top freezer-safe bag for up to 3 months. When ready to bake the cookies, roll the frozen peanut butter blossom dough balls in the granulated sugar and bake from frozen, adding about 3 minutes to the baking time before adding the chocolate Kiss.