Make brown butter. In a medium light-colored frying pan or skillet, melt the butter over low-medium heat. As the butter melt, it will begin to foam. Stir constantly to prevent the milk solids from sticking to the bottom and burning. The butter will go from yellow to golden brown quickly. Once the milk solids are toasty brown (dark brown, not black), and the butter smells nutty, remove from the heat.

Strain and transfer the browned butter into a heatproof bowl immediately. This will prevent the residual heat from the pan to continue cooking or burning the butter. Cool brown butter completely before using.

In a large bowl, add egg whites. Whisk slightly to break down the egg whites. Add castor sugar and honey. Whisk for 3 minutes or until the sugar is dissolved.

Sift in cake flour, hazelnut flour, and baking powder. Whisk until well combined.

Add cooled brown butter. Whisk until well incorporated.

Cover the bowl with a plastic wrap and chill the dough for at least 1 hour or overnight. You can skip this step, but chilling is recommended for the best flavor.

Remove the batter from the fridge. Using a spatula, mix to loosen the batter.

Transfer the batter into a piping bag and pipe the batter into the molds until 80-90% full. You can also alternatively spoon the batter into the molds.

Place 5 halved hazelnuts on top of each financier.

Bake for 12-15 minutes or until golden brown.

Remove financiers from the pan immediately and cool completely on a cooling rack. They are best eaten on the same day they are made.