Preheat oven to 350°F / 175°C. Lightly grease a nonstick hot dog-bun pan.

In a large bowl, whisk together the flour, ½ cup (100g) of the sugar, baking powder, and salt until combined. Set aside.

In a separate bowl, stir together the egg yolks, oil, orange juice, orange zest, and vanilla.

Add the dry ingredients to the egg yolk mixture and whisk together until smooth. Set aside.

In a stand mixer fitted with the whisk attachment, combine the egg whites and cream of tartar and beat on high speed until medium peaks form, about 2 minutes. Turn the speed to medium-low and slowly sprinkle in the remaining ¼ cup (50g) sugar to create a French meringue. Turn to high speed, beat until stiff, glossy peaks form, 1 to 2 minutes more.

Stir ⅓ of the meringue mixture into the egg yolk mixture to loosen it up. Then, fold the remaining meringue into the yolk mixture with a rubber spatula.

Fit a 16-inch pastry bag with a large round tip, pour the batter into the bag, and pipe into the prepared pan, filling each mold only ⅔ full.

Bake until golden and a tester comes out clean, 15 to 20 minutes. Invert the pan and tap gently to remove the cakes onto parchment paper. Let cool completely.

In a stand mixer fitted with the paddle attachment, combine the confectioners’ sugar and butter and beat on low speed until combined.

Fit a 12-inch pastry bag with a Bismark piping tip and fill with frosting. Inject frosting from the bottom of each cake by poking the tip into it about ¾ of the way through—fill until the cake begins to bulge. Repeat injecting the frosting every ½ inch.

Serve the cake immediately or store in the refrigerator, covered, up to 24 hours. If refrigerated, bring the cake to room temperature before serving.