Preheat the oven to 375˚F. Line a cookie sheet with parchment paper and set aside.
In a medium bowl, mix together the flour and baking soda. Set aside.
In a large bowl, cream together the butter, peanut butter, brown sugar and 1/2 cup granulated sugar until light and fluffy. Mix in the eggs.
Add in the vanilla and milk, and mix until fully incorporated.
Slowly mix in the dry ingredients until fully combined.
Pour the 1/4 cup of white sugar into a small bowl.
Using a cookie scoop, scoop the dough onto your hand and roll into a ball. Roll in the sugar and place on the prepared cookie sheet. Press your index finger in the centre to make a dent.
Bake in the preheated oven for 10-15 minutes, or until cookies are golden brown.
Remove from oven and immediately press the kisses in the centre of the cookies. Transfer to wire racks to cool completely.