To make your own almond flour, put no more than 8 ounces of blanched slivered almonds in a food processor and blend, stopping often to stir the almonds around to redistribute them, until very fine; be careful not to pulverize them into a paste. Strain them through a medium strainer and regrind any pieces of almonds that remain in the strainer.
Preheat the oven to 325°F.
Lightly spray 36 1 oz. barquette molds or Fleximolds and place them on a baking sheet.
Melt the butter over medium heat and continue to cook, swirling the butter until it is a rich golden brown with a nutty fragrance. Pour into a small bowl and set aside.
Combine the sugar, almond flour, salt, and flour in the bowl of a mixer fitted with the paddle attachment.
Add the egg whites and beat at medium speed for about 1 minute, until well combined.
Mix in the butter.
Note: If using homemade almond flour, place it with the granulated sugar in a food processor. Blend to combine.
Spoon about 1 tablespoon of batter into each mold, filling it about 3/4 full.
Sprinkle almonds on top of each mold. Place the baking sheet in the oven and bake for 20–25 minutes, or until tops are golden brown.
Remove from the oven and let cool, then remove the financiers from the molds.
Top with sliced almonds and dust the tops of the financiers with confectioner’s sugar.