Preheat your oven to 350°F (175°C) and prepare a large baking pan by lining it with parchment paper.
In a medium bowl, sift together the cake flour, cocoa powder, baking powder, and salt (and espresso powder if using).
In a separate bowl, beat the egg yolks with granulated sugar until the mixture is thick and pale. Stir in the vanilla extract.
Gently fold the dry ingredients into the egg yolk mixture until just combined.
In another bowl, whip the egg whites until stiff peaks form. Carefully fold the whipped egg whites into the batter, ensuring not to deflate the mixture.
Pour the batter into the prepared baking pan and spread it evenly. Bake for about 12-15 minutes or until the cake springs back when touched.
Once baked, remove the cake from the oven and immediately dust the top with powdered sugar. Carefully roll the cake up from one end while it's still warm, using the parchment paper to help. Let it cool completely.
Once cooled, unroll the cake gently and spread whipped cream filling evenly over the surface. Roll the cake back up tightly and place seam-side down on a serving platter.
Frost the log with chocolate ganache and decorate with meringue mushrooms, sugared cranberries, and rosemary sprigs as desired.