Preheat your oven to 350°F (175°C).
Grease a 10x15 inch jelly roll pan and line it with parchment paper.
In a bowl, whisk together flour, cocoa powder, and salt.
In a separate bowl, beat eggs and sugar until pale and thick.
Gently fold in the dry ingredients into the egg mixture.
Add the melted butter and vanilla, mixing until well combined.
Pour the batter into the prepared pan, spreading it evenly.
Bake for 12-15 minutes until the cake springs back when touched.
Once baked, remove the cake and let it cool for 5 minutes.
Dust with powdered sugar, then roll the cake with the parchment paper. Let it cool completely.