Preheat oven to 375 degrees.*
Combine butter, peanut butter, 1/2 cup sugar and brown sugar in a bowl and cream together with an electric mixer for 2-3 minutes. Add in egg, milk and vanilla and beat with mixer to combine.
Add in flour, baking soda and salt, and stir to combine ingredients. The flour mixture should all be absorbed into the peanut butter mixture, but do not overmix.
OPTIONAL – The dough can be covered and chilled for one hour if desired. This helps prevent cookies from spreading and deeps the flavor, but it is not required. If chilling, do not preheat the oven until ready to bake.*
Divide the dough into four even parts, using each of the four portions to make 12 cookie dough balls. Roll dough into 1″ balls.Pour remaining sugar into a small bowl or saucer and roll each dough ball in sugar.
Place cookie dough balls onto a baking sheet, at least 2″ apart, and bake until they start to lightly brown and puff up, about 6 to 8 minutes. Remove baking sheet and working quickly, gently press an unwrapped kiss into the center of each cookie. Return to the oven for an additional 2 minutes, until light golden brown.
Remove from oven and place plan on a wire rack to cool. once cool, store in an airtight container.