Stuffing cookies with little surprises is always a treat for kids and adults. I'm sure you will rank this peanut butter cookie among your favorites. Chocolate and PB go together well with these soft and chewy cookies.
In a medium bowl, whisk together flour, salt and baking soda. Set aside.
In a large mixer bowl, beat butter, peanut butter and brown sugar on medium high speed until light and fluffy, about 4-5 minutes. Turn mixer down to low and add milk, vanilla and egg. Mix until combined then turn up to medium high for one minute. Scrape down sides of bowl and turn mixer on low.
Slowly add the flour mixture until just combined.
Measure a tablespoon of cookie dough and roll in your hands a moment, then flatten it in your palm. Place a Hershey's Drop candy in the center of the cookie dough. Close the cookie dough around the filling, forming a ball. Roll gently in your hands and place on the cookie sheet. Flatten slightly in crisscross pattern with tines of fork.
Bake for 7-9 minutes, or until set and just beginning to brown. DO NOT OVERBAKE. Cookies will appear puffy when they come out of the oven and will relax and sink a little as they cool. Cool 3-4 minutes on baking sheet. Remove cookies to racks to cool completely.