Preheat oven to 375 degrees. Place parchment paper on baking sheet and set aside.
In a medium bowl, whisk together the flour, baking soda and salt and set aside.
In a large bowl with a stand mixer or electric hand mixer, beat the butter and peanut butter together until well combined, about 2 minutes. Add the granulated sugar and brown sugar and and beat until light and fluffy, at least 3 minutes. Add the egg, milk and vanilla and beat until combined. Turn the mixer on low and add half of the dry ingredients into the wet ingredients and beat slowly until flour is partially incorporated. Turn the mixer up to medium-high and beat until flour is completely incorporated. Add the remaining flour and repeat the process until dough is completely combined. Dough will start to pull away from the bowl and stick to the paddle.
Using a little less than one tablespoon, shape the dough in one inch balls, roll in bowl of extra sugar and place on baking sheet about 2 inches apart. Bake for 8-10 minutes until slightly golden and edges turn golden brown. Cookies won't spread much.
When they're done, press the Hershey kisses into the warm cookie right out of the oven. Allow to cool on pan for 3 minutes and transfer to wire rack to cool completely. Hershey kisses will be warm and melted. Allow to cool completely on wire rack until Hershey Kisses are set.