[T]he cherub, alas, proved to be pasted on tough gingerbread which was too hard for many to bite into.

Nabokov’s image contrasts an alluring surface (“the cherub”) with an unyielding substance (“tough gingerbread”). The metaphor suggests a work, idea, or persona that advertises sweetness, innocence, or decorative charm, yet proves difficult to “consume” or appreciate—too dense, resistant, or demanding for many readers. The phrasing implies a wry disappointment: what looked like an easy delight turns out to require effort, strong teeth, or a taste for hardness. More broadly, it captures Nabokov’s recurring skepticism toward sentimental veneers and his insistence that genuine aesthetic experience may be challenging rather than immediately gratifying.