Make the brown butter: Warm the butter in a small stainless steel saucepan over medium heat until completely melted and simmering. Keep on cooking over low heat, swirling the pot from time to time, until the milk solids at the bottom of the pot turn a light brown color and the concoction gives off a delicious hazelnut aroma.
When the butter is browned, immediately remove the pan from the heat and pour in a small bowl, scraping down every last bit of the caramelized solids from the bottom of the pan. Let the brown butter cool for 10 minutes.
In a large mixing bowl, whisk together the almond flour, all-purpose flour, granulated maple sugar, baking powder, and salt. Add the egg whites and whisk until they are fully incorporated and the mixture is thick and somewhat sticky. Mix in the brown butter, whisking gently at first to incorporate, then giving it a vigorous stir to allow the batter to fully come together. At this point, the maple financier batter can be transferred to an airtight container and refrigerated for up to 1 week.
Bake the financiers: Preheat the oven to 350°F (175°C). Line a mini muffin pan with parchment paper liners or grease a financier pan with softened butter, then sprinkle with flour and tap out the excess. (Make sure to grease the pan even if it is made of silicone because the texture of financiers tend to be delicate and sticky.)
Drop 1 tbsp (15 ml) of dough in each mini muffin cup. Garnish each financier with 1 pecan half, if desired. Bake maple financiers for about 12 minutes: the financiers are done when they are golden brown around the edges and set in the center. (If you refrigerated the financier batter, you will need to add 2-3 minutes to the baking time.)Let the maple financiers cool for 10 minutes in the pan, then transfer to a cooling rack to cool completely.
SERVING: Serve maple financiers at room temperature. For an extra-indulgent maple touch, serve the financiers with a small bowl of warm maple syrup for dipping.
STORAGE: Store financiers in an airtight container at room temperature for up to two days. You can also refrigerate financiers in an airtight container for up to 1 week, and freeze for up to 1 month. To return cold financiers to their freshly baked glory, warm in a 325°F (160°C) oven for 5 minutes, let cool slightly, then enjoy.
You can use different types of nut flours to switch up the flavor of your maple financiers. Classic financiers are made with almond flour—finely ground almonds, that is—but you can use ground walnuts, hazelnuts, and pecans, too. Make sure the nuts are ground to a very fine, smooth texture. If you grind your own nuts, make sure to process them along with the maple sugar to avoid turning the nuts into butter.
If you don't want to be stuck with leftover egg yolks, you can use egg whites from a carton (liquid egg whites) to make maple financiers. Refer to the manufacturer's packaging instructions to find out the quantity of liquid egg whites you need to substitute 4 large egg whites, or simply weigh the liquid egg whites to use the precise quantity required in the recipe (120 g).
Wondering what to make with leftover egg yolks? Here are some ideas: