Preliminaries: Freeze the egg whites, and let them defrost naturally before you need them.
Make the browned butter: Put the butter in a pan and heat it up over medium heat. When it is foamy and the color starts to change, turn the heat down to low.
When the butter starts bubbling, it will start to smell browned and nutty. Shake the pan occasionally to check on the color of the butter.
When the butter is the color of hazelnuts (a pretty brown), filter it through a strainer and leave to cool.
Thinly grease the financier molds with butter, and dust with bread flour. Preheat the oven to 200 °C.
Combine the egg whites with sugar, and add the maple syrup and salt.
Sift the hazelnut powder and cake flour together and add to the Step 5 bowl. Mix well.
Gently pour in the lukewarm browned butter, and mix well again.
Spoon the batter into the molds about 80% full. Put pieces of marron glacés of the size you like in the middles.
Bake in a 200 °C oven for 13 minutes. When the batter has puffed up a bit and the tops are browned, the financiers are done.
Take them out of the molds immediately and cool on a rack. When they have cooled down completely, put into a tightly sealed container and rest for 1-2 days to finish.
These are broken marron glacés. They are quite cheap. Find them at stores that sell baking ingredients and so on (such as Kaldi and Fujisawa Shoten in Japan).
I don't actually own financier molds, so I always use madeleine molds instead. The flavor doesn't change and the results are very pretty. Use your favorite mold for this.
There's a tender piece of marron glacé inside, and the financiers are really moist and delicious.
Story Behind this Recipe
I found some broken marron glacé on sale, so I decided to make financiers with them. I tried combining hazelnut powder and maple syrup in the batter, which was a perfect combination. These financiers have a very fall flavor.
The butter should be browned well to go with the hazelnut powder. Pass the butter through a fine-meshed tea strainer. In addition, slowly pour the butter into the bowl with the other batter ingredients, so that the small burned bits in the bottom of the container don't get transferred. The financiers are delicious when freshly baked, or the next day, or the day after that.