Preheat oven to 350°F (175°C).

Line a 10×15-inch jelly roll pan with parchment paper, leaving extra on the sides to lift the cake later.

Make the Batter

Beat eggs with an electric mixer until thick and pale (about 5 minutes).

Gradually add sugar and vanilla; continue beating until fluffy.

In another bowl, sift together cocoa powder, flour, baking powder, and salt.

Gently fold dry ingredients into the egg mixture until combined.

Bake

Spread batter evenly into the prepared pan.

Bake for 10–12 minutes, or until cake springs back when lightly touched.

Roll While Warm

Place a clean kitchen towel on a flat surface and dust generously with powdered sugar.

Turn the hot cake onto the towel, peel off parchment, and roll it up (cake + towel) starting from the short side.

Let cool completely while rolled.

Make the Filling