Preheat the oven to 350F (180C).
Make the brown butter: In a saucepan, add the butter and cook on medium heat until amber, this can take about 5-7 minutes. Set aside to cool.
Sieve the flour, almond flour, powdered sugar, and salt.
Slightly whisk the egg whites until foamy.
Fold in the egg whites with the dry ingredients until smooth batter.
Add the vanilla and browned butter.
Mix with a silicone spatula or a whisk until smooth. The batter will be loose, similar to pancake batter.
Grease the muffin pan with the soft butter using a pastry brush, or use cooking spray instead of butter.
Using a cookie dough scoop or a piping bag, fill each muffin cavity about ¾ from the top.
Sprinkle some of the shaved almonds on top.
Bake at 350F for 20 minutes, or until the edges are golden brown and a toothpick comes out clean from the center.
Let them cool on a wired rack for 5-10 minutes before enjoying.