Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, beat the egg yolks with 1/4 cup of sugar until pale and thick. Mix in vanilla.
In another bowl, beat the egg whites with the remaining 1/4 cup of sugar and salt until stiff peaks form.
Gently fold the sifted flour and cocoa powder into the yolk mixture, then carefully fold in the egg whites.
Spread the batter evenly on the prepared baking sheet and bake for 12-15 minutes, or until the cake springs back to the touch.
While the cake is baking, whisk together the heavy cream, cocoa powder and powdered sugar until it holds stiff peaks for the filling and frosting.
When baked, remove the cake from the oven and roll it up with parchment paper, allowing it to cool in a rolled shape.
Once cool, unroll the cake and spread a layer of cream filling over the surface. Roll the cake again without the parchment paper.
Cover the rolled cake with the remaining whipped cream, mixed with cocoa powder for a chocolate frosting appearance.
Decorate with chocolate shavings and other holiday garnishes as desired. Chill in the refrigerator before serving.