What finger-shaped sponge biscuits are a principal ingredient in tiramisu?

The finger-shaped sponge biscuits that are a principal ingredient in tiramisu are ladyfingers.

Ladyfingers are light, dry, sweet sponge biscuits also known as savoiardi in Italian, boudoirs in French, and sponge fingers in British English. Their porous texture allows them to absorb liquid without immediately collapsing, making them ideal for tiramisu, where they are soaked in coffee or espresso and layered with mascarpone cream.

The biscuits are traditionally made by separating eggs, whipping the whites and yolks with sugar, then folding in flour. They usually contain no chemical leavening; trapped air from the beaten eggs creates their sponge-like structure. Powdered sugar sprinkled over the piped batter forms a delicate crust during baking.

Ladyfingers are also used in trifles, charlottes, and dessert linings. They are often confused with ordinary tea biscuits, but their airy structure is crucial to classic tiramisu. The biscuits are said to have originated at the 14th-century court of Savoy, where they were served to visitors and honored guests.