Gently brown the butter by heating it in a small saucepan over medium heat. Allow the butter to bubble until the foam cooks off and develops a nutty aroma, and small browned bits begin to appear on the bottom of the pan. Be careful to not let it burn. Strain out the chunky bits and set the butter aside.
Combine the powdered sugar, almond flour, all-purpose flour, cocoa powder, and salt in a bowl. Mix well. Stir in the applesauce and half of the egg whites, mixing just until combined. Add the remaining egg whites and the browned butter, again stirring just until combined. Press a piece of plastic wrap to the surface of the batter and let rest in the refrigerator overnight.
The following day, preheat the oven to 375°F/190°C. Lightly butter a mini-muffin pan and fill each cup three-quarters full with batter. Do not overfill, especially if you’re baking in a convection oven, as the movement of the air will blow the tops sideways.
Top each financier with 6 to 8 pieces of candied orange peel and 4 or 5 almond slices. Bake for 9 to 11 minutes. Financiers are done when they are springy to the touch. Do not overbake or they will lose their signature moist texture.