The French dessert that is a small almond cake often baked in a rectangular mold is a financier.
A financier is a compact, moist cake made with ground almonds or almond flour, egg whites, powdered sugar, flour, and beurre noisette—brown butter with a toasted, nutty aroma. Its small rectangular shape is especially traditional, although financiers may also be baked in oval, round, or other molds.
The cake traces its ancestry to the Visitandine nuns of Lorraine and was popularized in the 19th century. The name is commonly linked to the rectangular mold’s resemblance to a gold bar. Another tradition connects it with pastry shops near the Paris stock exchange, where financiers supposedly appreciated a small cake that was easy to carry and eat.
A financier is not a macaron, which is a meringue-based sandwich cookie, nor a madeleine, whose shell-like shape and sponge-cake texture are distinctive. Financiers are also related to friands, especially in Australia and New Zealand, but the French version is most strongly associated with browned butter, almond flavor, and its petite bar-like form.