Preheat your oven to 350°F (175°C) and grease a 15x10-inch jelly roll pan.
In a mixing bowl, beat eggs and granulated sugar until thick and pale.
Sift together cocoa powder, flour, baking powder, and salt; gradually fold into the egg mixture.
Spread the batter evenly in the prepared pan.
Bake for 12-15 minutes until the cake springs back when touched.
Once baked, remove from oven and immediately roll the cake in a clean kitchen towel dusted with powdered sugar.
Let it cool completely while rolled up to maintain shape.
Whip the heavy cream with powdered sugar and vanilla until soft peaks form.
Unroll the cooled cake, spread whipped cream evenly, then re-roll gently.
Frost the outside of the rolled cake with remaining whipped cream and decorate with chocolate shavings.