Preheat the oven to 350°F (175°C). Line a 10x15-inch jelly-roll pan with parchment and lightly grease.

Sift together flour, cocoa powder, baking powder, and salt into a bowl; set aside.

In a mixing bowl, whisk egg yolks with half the granulated sugar until pale and slightly thick. Stir in 1 teaspoon vanilla.

In a separate clean bowl, beat the egg whites to soft peaks, then gradually add the remaining granulated sugar and beat to glossy, medium-stiff peaks.

Fold the dry ingredients into the yolk mixture in two additions, using gentle strokes to keep air in the batter.

Fold a quarter of the beaten egg whites into the batter to loosen it, then gently fold in the remaining whites until no streaks remain. Don’t overmix.

Spread the batter evenly into the prepared pan, smoothing the top with an offset spatula.

Bake for 10–12 minutes, until the cake springs back slightly and a toothpick comes out clean. Avoid overbaking — the cake must stay pliable.

Immediately after removing from the oven, dust a clean kitchen towel with powdered sugar. Turn the warm cake out onto the towel, peel off the parchment, and trim any uneven edges.

Starting at a short side, roll the cake and towel together into a tight spiral. Let it cool rolled up.

Whip the cold heavy cream with powdered sugar and vanilla until medium peaks form. Taste and adjust sugar.

Carefully unroll the cooled cake. Spread an even layer of whipped cream, leaving a 1/2-inch border to prevent overflow.

Re-roll the cake without the towel, wrapping it tightly. Chill at least 30 minutes to firm the filling.

Optional: warm ganache slightly and drizzle or spread over the cooled roll for a glossy finish. Chill briefly to set.