Preheat the oven to 180°C (350°F). Line a baking sheet (about 10×15 inch) with parchment paper.

In a bowl, beat eggs and granulated sugar until thick and pale, about 5 minutes. Add vanilla extract and mix.

Sift cocoa powder, flour, and salt together. Gently fold the dry ingredients into the egg mixture, ensuring not to deflate the batter.

Pour the batter into the tray and spread evenly. Bake for 10-12 minutes until the top springs back when touched.

While warm, invert onto a clean towel dusted with cocoa powder. Gently peel away the parchment and roll the sponge with the towel. Cool completely.

Beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Unroll the cooled sponge and spread the cream over it, leaving a small border. Reroll the sponge without the towel.

Heat the cream until it just begins to boil. Pour over the chopped chocolate and let sit for 2 minutes.

Mix until smooth and let it cool slightly until thickened but pourable.

Pour the ganache over the cake, spreading evenly. Cool in the refrigerator until set.