Very closely adapted from The New York Times. Note that if you use hollow chocolates, like the bunnies, chicks and sheep that I used, some of them may collapse on themselves from melting (!). Only a few did and I chose not to photograph those.
Whisk together flour, baking soda and salt; set aside.
Using an electric mixer, cream together the butter and peanut butter. Scrape the sides and bottom of the bowl, and then add the sugars. Beat until well combined and fluffy, about 3-4 minutes.
Scrape the sides and bottom of the bowl. Add the egg, milk and vanilla; beat until well blended.
Add the flour mixture in about 4 additions, mixing thoroughly on the lowest speed. Scrape the bowl as needed. Refrigerate the dough for at least 1 hour.
When you are ready to bake, preheat oven to 350 degrees. Line the cookie sheets with silicone mats or parchment paper.
Scoop out heaping tablespoon-sized balls of dough, roll them into a ball and then roll the balls in sugar. Place 12 balls per cookie sheet.
If you bake 2 cookie sheets at a time, place the oven racks in the upper and lower thirds of the oven. Bake at 350 F for 9-12 minutes, until the cookies have puffed, cracked a bit, and are golden brown.
Remove the cookies from the oven and immediately press a chocolate candy into the center of each cookie. Let the cookies rest on their sheet for 5 minutes and then move them to a cooling rack to cool completely. Make sure the melting chocolate sets completely before storing the cookies in single layers separated by wax paper in an airtight container.