the goods:
cake:
1 cup all-purpose flour, plus more for pans
5 large eggs plus 2 large egg yolks
3/4 cup granulated sugar
6 tablespoons unsalted butter, melted and cooled
filling:
2 large eggs, separated
2 cups mascarpone cheese, room temperature
1 cup confectioners' sugar
1/3 cup unsweetened cocoa powder
1 tablespoon orange zest
1/4 cup freshly squeezed orange juice
glaze:
6 ounces bittersweet chocolate, finely chopped
3/4 cup heavy cream
Make cake: Preheat oven to 450 degrees, with racks in upper and lower thirds. Coat two 10-by-15-inch jelly-roll baking pans with cooking spray. Line with parchment paper; coat with cooking spray. Dust with flour, tapping out excess. In a bowl, whisk together flour and 1/4 teaspoon salt.
In a large bowl, using an electric mixer, beat eggs, yolks, and sugar on medium-high, 2 minutes; increase speed to high and beat until pale and thick, 5 minutes. Sift flour mixture over egg mixture; with a large rubber spatula, fold together until almost blended. Pour butter down side of bowl, folding to combine.
Divide batter between pans; smooth with a table knife. Immediately transfer pans to oven and bake until cakes are golden brown and springy when pressed, 6 to 7 minutes, rotating pans halfway through. Let cool completely.
Make filling: In a large bowl, stir together egg yolks, mascarpone, sugar, cocoa, orange zest, and a pinch of salt. In another large bowl, using an electric mixer, beat egg whites and a pinch of salt until soft peaks form. With a large rubber spatula, fold one-thirds whites into mascarpone mixture; fold in remainder.
Invert cakes onto a work surface and gently peel off parchment. Using a serrated knife, trim edges off cakes, then cut each cross-wise into thirds. Place 1 cake layer, golden side up, on a platter; brush with orange juice and spread with a layer of filling. Repeat with remaining cake, orange juice, and filling, ending with a layer of orange-brushed cake. Refrigerate until set, about 30 minutes.
Make chocolate glaze: Place chocolate in a heatproof bowl. In a small saucepan, heat cream over medium-high; when bubbling around edge, pour over chocolate. Let stand 3 minutes, then whisk until shiny and smooth.
Pour glaze over top of cake and spread so it drips down sides. Spread glaze up sides to cover completely.
Refrigerate 1 hour.
Sprinkle with granulated sugar. Slice and serve!
