Sponge fingers are thin, finger-shaped sponge biscuits made from whisked egg yolks and caster sugar folded with flour, the crisp-chewy components of trifles and tiramisu. Known as ladyfingers or savoiardi in Italy, they are piped in neat lengths and dusted with sugar before baking to a pale gold. Their open crumb drinks up liquid eagerly, which is exactly their purpose: soaked in sherry for trifle, in coffee and liqueur for tiramisu, they become the melting layer that defines the dessert. Eaten plain they are light and simple, a nursery biscuit. Their structure is all egg foam, no chemical raising, which is why they stale quickly and are best used fresh or promptly soaked.