Preheat your oven to 350°F (175°C) and line a 15x10-inch jelly roll pan with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat the eggs and sugar on high speed until thick and pale, about 5 minutes. Add vanilla and espresso powder, mixing well.
Fold the dry ingredients into the egg mixture gently using a rubber spatula.
Melt unsalted butter and dark chocolate together until smooth. Allow to cool slightly, then fold into the batter.
Pour the batter into the prepared pan and bake for 12-15 minutes, until the cake springs back when touched.
Remove the cake from the oven and immediately turn it out onto a towel dusted with powdered sugar, rolling it tightly. Let cool.
Beat together butter, shortening, marshmallow fluff, and powdered sugar for the filling. Add heavy cream and mix until smooth.
Unroll the cooled cake and spread the filling evenly. Roll it back up without the towel, seam-side down.
Melt remaining chocolate, salted butter, and cream for the ganache until smooth. Pour over the rolled cake.
Chill the cake roll for at least 30 minutes to set the ganache. Slice and serve.
