01 - In a large mixing bowl, whisk together the flour, cocoa powder, sugar, yeast, and salt until evenly distributed.
02 - Pour in the lukewarm milk, add the softened butter, egg, and orange zest. Stir with a wooden spoon or dough hook until a sticky, cohesive dough comes together.
03 - Turn the dough onto a lightly floured surface and knead firmly for about 10 minutes, until the dough is smooth, satiny, and springs back when pressed.
04 - Transfer the dough to a lightly greased bowl, cover with a damp towel or plastic wrap, and let it rest in a warm, draft-free spot for 1 to 1½ hours, or until doubled in volume.
05 - Gently deflate the dough and divide it into 8 equal portions. Roll each piece into a plump oval and arrange on a parchment-lined baking sheet, spacing them about 2 inches apart. Cover loosely and let proof for 30 minutes until puffed.
06 - Preheat the oven to 350°F (180°C). Bake the buns for 18 to 20 minutes, until just set and the tops feel firm to the touch. Transfer to a wire rack and cool completely before filling.
07 - Heat 3½ tablespoons of the cream in a small saucepan until steaming but not boiling. Pour over the chopped dark chocolate and stir until a glossy ganache forms. Allow to cool to room temperature. Whip the remaining cream with the powdered sugar to stiff peaks, then gently fold in the cooled ganache until uniform.
08 - Using a sharp serrated knife, slice each cooled bun lengthwise, leaving one side attached as a hinge. Pipe or spoon a generous amount of chocolate whipped cream into each bun, allowing it to billow slightly above the edges.
09 - Dust the filled maritozzi generously with powdered sugar just before serving. Enjoy fresh.