Make brown butter by melting unsalted butter until golden brown.
Whisk with honey, espresso powder, vanilla, salt. Cool.
Whip egg whites, and gradually add sugar to soft peaks.
Fold in sifted flour and almond flour, into the mixture then and add the brown butter mixture.
Pour into small molds ( smaller than the tart rings). Optional: Add chopped nuts (walnut, hazelnut or both) on top of the batter.
Bake at 180°C for 12 mins, then 170°C for 5 mins.
Let them cool before removing from the molds.