01 - In a large mixing bowl, whisk together the flour, cocoa powder, granulated sugar, active dry 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 for approximately 10 minutes until the texture becomes smooth, elastic, and slightly tacky but no longer sticking to your hands.
04 - Transfer the dough to a greased bowl, cover tightly with plastic wrap or a damp kitchen towel, and let it rest in a warm, draft-free spot for 1 to 1½ hours until doubled in volume.
05 - Punch down the risen dough and divide it into 8 equal portions. Shape each piece into an oval bun and arrange on a parchment-lined baking sheet, leaving space between them. 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 spring back lightly when touched. Transfer to a wire rack and cool completely.
07 - Gently heat about 3 tablespoons of the heavy cream in a small saucepan until steaming. Pour it over the finely chopped dark chocolate and stir until a smooth ganache forms. Allow to cool to room temperature. Whip the remaining heavy cream with the powdered sugar to stiff peaks, then fold in the cooled chocolate ganache until uniformly combined.
08 - Using a sharp serrated knife, slice each cooled bun lengthwise, leaving one side attached as a hinge. Generously pipe or spoon the chocolate whipped cream into each bun.
09 - Dust the filled maritozzi generously with powdered sugar and serve immediately.