Preheat oven to 450 degrees. Brush the inside of a 13 1/2-by-4-inch tart pan that has a nonremovable bottom with melted butter; transfer to freezer.
Using a food processor, pulse almonds until finely ground. In a large bowl, combine ground almonds, confectioners' sugar, flour, salt, and orange zest. Add egg whites, and whisk to combine. Slowly stir in butter.
Remove tart pan from freezer. Pour batter into pan; place on a baking sheet. Bake until dough just begins to rise, about 10 minutes. Reduce oven heat to 400 degrees and continue baking 7 to 8 minutes more, until financier begins to brown. Turn off oven, and let cake stand in oven until firm, about 10 minutes. Transfer pan to a wire rack to cool completely.
Invert financier onto rack; reinvert, and slice into 6 pieces. Garnish top with candied orange peel, and dust with confectioners' sugar.