Double Chocolate Oriolos

These amazing cookies are named for Richard Oriolo, beloved art director and designer of all of my books, because he simply cannot eat enough of them. Perhaps it’s because they are intensely chocolatey and buttery yet extraordinarily light, and so easy to swallow. The chocolate buttercream topping is silky smooth under its crown of crunchy toasted walnuts. It stays spreadably soft for hours at room temperature but hardens overnight or on refrigeration just enough