Reese's peanut butter pieces, 1 per cookie if you like, or cut in half along the equator if you are going to be packing them.
How to make it
Preheat oven to 350 degrees.
Melt 1 stick butter and put the other in the same container to soften, about 5 m.
Cream butter with sugars until light and fluffy.
Add eggs one at a time, beating until smooth after each.
Add peanut butter!
Using a shield guard if your mixer has one, add dry ingredients and beat briefly but hard until combined.
Chill dough 20 m.
Form dough into walnut-sized balls; place on a greased/Silpat-lined cookie sheet; mash crosswise with a fork to flatten.
Bake 8 min--should still be quite soft, maybe another minute if your oven is slow, but no longer.
Top each cookie with its Reese's piece.
Let the cookies cool on the cookie sheet at least 5 m, then transfer to a rack. They will firm up as they cool. If the Reese's pieces are not firming up, set the cookies in the path of an electric fan.