Sift flour, baking soda, and salt and set aside.
Mix the butter and the peanut butter until well combined.
Add the granulated sugar and the brown sugar and mix.
Add the milk, egg, and vanilla.
Add the flour and mix until combined.
Shape the dough into one inch balls and roll in the extra granulated sugar.
Place them on the baking sheet lined with parchment paper or a Silpat 2" apart.
Chill them in the fridge for 10-30 minutes before you bake them. Remember, the warmer the dough balls are the more the cookies will spread.
Bake them at 350 degrees for 6-9 minutes. When the edges start to turn light brown remove them from the oven and place a kiss in the center of each cookie immediately.
Let them cool completely.