Preheat oven to 350°F (177°C). Grease a 12×17-inch baking pan with nonstick spray or butter, then line it with parchment paper so the cake seamlessly releases in step 7. Spray or grease the parchment paper, too. We want an extremely nonstick surface for this cake roll.

Using a fine mesh sieve, sift the cake flour, cocoa powder, baking powder, and salt together. Set aside.

Using a hand mixer or a stand mixer fitted with whisk attachment, beat the egg whites and 1/4 cup (50g) granulated sugar together on high speed for 4–5 minutes or until foamy-looking medium peaks form. (Medium peaks have a slight droop, and aren’t quite stiff.) Transfer to another bowl.

Using the same mixing bowl you just had the egg whites in (no need to clean it), add the egg yolks and remaining sugar. Mix on high speed for 1 minute, and then add the oil, milk, vanilla, and espresso powder. Beat together on high speed for 2 minutes. Mixture will be thin and a little bubbly on top. Add half of the whipped egg whites into the egg yolk mixture. Mix on low speed for 10 seconds. Repeat with remaining egg whites and mix on low for 10 seconds.

Sift in the flour mixture, and then fold the batter together with a silicone spatula until combined. Do not over-mix. Batter is light and fluffy.

Spread batter evenly into prepared pan. It will be a very thin layer. Shimmy the pan on the counter to smooth out the top. Bake for 12–14 minutes or until the top of the cake lightly springs back when touched with your finger. Do NOT over-bake.

As the cake bakes, place a piece of parchment paper (larger than the cake) or a thin kitchen/tea towel flat on the counter. (Note: I find a kitchen/tea towel is better to help prevent cracking.) Using a fine mesh sieve, dust parchment/towel with about 2 Tablespoons of cocoa powder. Once the cake comes out of the oven, quickly run a knife around the edges to loosen it from the pan. Immediately invert it onto the parchment/towel. Peel off the parchment paper that was on the bottom of the cake as it baked. Starting with the narrow end, begin tightly rolling the hot cake up with the parchment/towel. Do this slowly and gently. The cake will be warm. Allow the cake to cool completely at room temperature rolled up in the parchment/towel, about 3 hours. Feel free to set it aside for up to 1 day. (Note that letting it cool in the refrigerator and then unrolling it when it’s cold will cause it to tear and break. I strongly recommend letting it cool slowly at room temperature.)

Using a hand mixer or a stand mixer fitted with a whisk attachment, whip the heavy cream, sugar, and vanilla extract on medium-high speed until medium to stiff peaks form, about 2–3 minutes. Then beat in the marshmallow creme, if using.

Slowly and gently unroll the cake. Spread whipped cream evenly on top, leaving about a 1/2-inch border around the cake. Gently roll the cake back up, without the parchment/towel this time. Place on a wire rack set on a baking sheet (to catch any drips of ganache). Set aside on the counter or in the refrigerator as you prepare the ganache.

Place chopped chocolate and corn syrup, if using, in a medium bowl. Heat the cream in a small saucepan until it begins to gently simmer. (Do not let it come to a rapid boil—that’s too hot.) Pour over chocolate, then let sit for 2–3 minutes to gently soften the chocolate. Slowly stir until completely combined and chocolate is completely melted. Ganache is smooth and glossy.

Pour ganache all over cake roll. Feel free to spoon up any dripped ganache and spoon over the cake again. Refrigerate for at least 30–60 minutes before slicing and serving.

Cover leftover cake and store in the refrigerator for up to 3 days.