Melt the butter over medium-low heat until it turns brown, then let it cool.
Sift together almond flour, cake flour, and baking powder.
Put sugar and salt in a bowl, add egg whites, and mix with a whisk.
Add the sifted dry ingredients to the egg white mixture and gently combine.
Add the melted brown butter and vanilla bean, and mix well.
Rest the batter in the refrigerator for 30 minutes.
Brush the financier molds with butter and fill them up to 80% with the batter.
Bake in a preheated oven at 180°C (356°F) for 15 minutes.
Remove from the molds after completely cooling.