Beat butter, peanut butter, 1/2 cup granulated sugar and light brown sugar.
Add egg, milk and vanilla
Beat well.
Slowly add flour, baking soda and salt.
Chill dough one hour wrapped.
Preheat oven to 375 degrees.
Line cookie sheet with parchment.
Roll dough into 1-inch balls.
Roll each in the sugar and place on sheet.
Bake 8-9 minutes.
Remove and immediately lightly press a kiss/pb cup in the center.
Let cool.