These buttery French tea cakes are known for being shaped like a bar, but they taste good in any form.
Preheat oven to 350 degrees. Spread almond flour evenly on a rimmed baking sheet. Toast until browned, 8 to 10 minutes. Remove from oven, and raise heat to 375 degrees. Meanwhile, melt butter in a small saucepan over medium heat until browned, about 8 minutes. Immediately transfer to a bowl with browned bits. Let cool.
Combine flours and sugar in the bowl of a mixer. Add whites, and beat on medium speed until combined and sugar is incorporated. With machine running, pour in browned butter (with brown bits) in a slow, steady stream. Continue to beat for 3 minutes. Batter can be refrigerated for up to 3 days.
Coat a cast-iron pan with oil or cooking spray, and fill halfway with batter. Bake until dark gold (time will vary depending on size of pan). Remove from oven, and immediately transfer financiers from pan to a wire rack. Let cool. Coat each with glaze if desired, or serve immediately.