1-1/2 cups (350 milliliters) mascarpone, at room temperature
15 centimeter vanilla pod, seeds only
1/4 cup (60 milliliters) brewed espresso, cooled to room temperature
60 milliliters dark chocolate, coarsely grated
5 centimeter cookie cutter
Piping bag fitted with a donut-filler tube nozzle
Heat milk until warm. Add yeast and one tablespoon (15 milliliters) sugar and stir in. Let sit for five minutes until foaming.
Combine flour and salt in a bowl.
Transfer yeast mixture to bowl of a stand mixer fitted with a paddle attachment. Add remaining sugar, butter, and eggs and mix until combined. Switch paddle attachment for hook attachment. Add flour mixture slowly, mixing at a low speed, until a smooth dough forms.
Place dough in a bowl greased with oil, cover, and let rest one hour.
Transfer dough to a lightly-floured surface and punch down. Roll out until roughly 1.25 centimeters thick. Cut out rounds from dough using a five centimeter cookie cutter.
Add vegetable oil to a deep, heavy-bottomed saucepan. Heat oil to 350 F (175 C). Carefully add donuts to vegetable oil, working in batches, and fry for about 1-1/2 minutes or until golden brown on the bottom. Use a metal spatula or slotted spoon to flip to the other side and fry for another one to 1-1/2 minutes. Flip back to the other side and repeat one more time, then remove with a slotted spoon to a paper towel-lined plate.
Combine sugar and espresso powder in a small bowl. When donuts are cool enough to handle, but still warm, roll in espresso sugar to coat, then set aside to cool completely.
Beat whipping cream until stiff peaks form. In a separate bowl, beat together icing sugar and mascarpone until fluffy. Stir in vanilla seeds and espresso, then fold in the whipped cream and dark chocolate. Transfer to a piping bag. (Note: the round tip of your piping bag must be larger than the pieces of your chocolate, or they will clog the nozzle when you attempt to pipe).
Press nozzle of piping bag gently into cooled donuts and fill with tiramisu cream. Repeat until all donuts are filled. Serve fresh.