How to Make It
Preheat oven to 350°F. Stir together unbleached all-purpose flour, almond flour, baking powder, and salt in a medium bowl; set aside. Place eggs, oil, brown sugar, 1 cup granulated sugar, and 1 tablespoon cinnamon in bowl of a heavy-duty stand mixer fitted with a paddle attachment. Beat on medium speed until combined, about 2 minutes. Stir in orange juice and vanilla extract.
With mixer running on low speed, gradually add flour mixture, beating until just combined. Stir in chocolate. (At this point, the dough should be stiff enough to loosely shape—not as stiff as cookie dough, but not as loose as cake batter.) Spoon dough out at a diagonal (corner to corner) onto a parchment paper–lined rimmed baking sheet. Using wet hands, shape dough into a 14- x 7-inch loaf. (Loaf will spread considerably while baking; center on baking sheet as much as possible.)
Bake in preheated oven until loaf is lightly browned and set, 24 to 26 minutes. Let loaf cool on baking sheet 5 minutes. Using a serrated knife, cut loaf crosswise into 1/2-inch-thick slices. Transfer slices, cut sides down, to 2 parchment paper–lined baking sheets. Bake slices at 350°F until golden brown, 12 to 14 minutes.
Stir together remaining 1/2 cup sugar and remaining 1 teaspoon cinnamon. Sprinkle about 1/4 teaspoon cinnamon-sugar over each hot mandel bread slice. Transfer slices to a wire rack, and let cool completely, about 1 hour.