In a small bowl, cream together softened butter, brown sugar, and granulated sugar until lightened and fluffy.
Add in peanut butter and mix until combined.
Mix in vanilla extract and egg yolk until smooth.
Sift flour, baking soda, baking powder and salt into the butter mixture, and mix until a soft dough forms.
Shape and bake:
Divide dough and roll into 8 small balls, about 1 tablespoon each.
Roll each ball in granulated sugar and place onto the baking sheet, spacing evenly.
Bake at 375°F/191°C for 8-10 minutes, until edges are set but centers are slightly soft.
Press an unwrapped chocolate kiss into the center of each cookie immediately after removing from the oven. The cookie will crack slightly around the edges.
Decorate with festive nonpareils, if desired.
Cool on the baking sheet for 5 minutes, and then transfer to a wire rack to completely cool before storing in an airtight container.