Ground almonds are traditional in financiers, but hazelnuts, pistachios, or other nuts work beautifully. The nuts should be finely ground but not turned to paste. Store-bought almond flour works well. Ground nuts provide moisture, richness, and structure to the delicate sponge. They also help create the characteristic slightly chewy texture that differentiates financiers from regular sponge cakes. Toast nuts lightly before grinding for enhanced flavor.