First Step: Prepare Baking Equipment and Preheat Oven. Preheat your oven to 350°F (177°C). Grease a 10×15-inch jelly roll pan and line it with parchment paper, greased or sprayed to prevent sticking.

Second Step: Sift Dry Ingredients. Sift together cake flour, cocoa powder, baking powder, and salt to ensure even mixing and avoid lumps.

Third Step: Whip Egg Whites. Beat egg whites with 1/4 cup (50g) sugar until medium peaks form. Set aside carefully to preserve the airiness.

Fourth Step: Mix Yolks and Wet Ingredients. Beat egg yolks with remaining 1/2 cup (100g) sugar until pale and thick. Add vegetable oil, buttermilk, vanilla extract, and espresso powder if using.

Fifth Step: Fold in Whipped Whites and Dry Ingredients. Gently fold half of the egg whites into the yolk mixture, then add the dry ingredients. Carefully incorporate the remaining whites, folding softly to maintain a light texture.

Sixth Step: Bake the Sponge. Spread the batter evenly in the prepared pan. Bake for 12-14 minutes, until the cake springs back lightly when touched. Avoid overbaking to keep the sponge moist and flexible.

Seventh Step: Roll the Warm Cake. Immediately loosen edges, invert onto cocoa-dusted parchment or a clean kitchen towel, and peel off baking parchment. Roll the sponge with the towel from the short side, seam side down, and let cool at room temperature for around 3 hours to set the shape.

Eighth Step: Prepare Filling and Fill the Cake. Whip heavy cream with sugar and vanilla extract until medium to stiff peaks form, optionally fold in marshmallow creme for texture. Unroll the cooled sponge and spread the filling evenly, leaving a border. Re-roll the cake carefully without the towel, filling cracks with cream if needed.

Final Step: Make Ganache and Finish. Heat cream to a simmer, pour over chopped chocolate, let sit 2-3 minutes, then stir until smooth. Add corn syrup if desired for shine. Pour ganache over the rolled cake. Refrigerate for 30-60 minutes to set before slicing and serving.