Preheat the Oven:
Preheat your oven to 350°F (177°C). Grease a 12×17-inch baking pan with nonstick spray or butter, then line it with parchment paper. Grease the parchment paper as well to ensure an extremely nonstick surface.
Make the Cake:
Sift the flour, cocoa powder, baking powder, and salt together using a fine mesh sieve. Set aside.
In a separate bowl, using a hand mixer or stand mixer with a whisk attachment, beat the egg whites with ¼ cup (50g) granulated sugar on high speed for 4-5 minutes, until medium peaks form. Transfer to another bowl.
In the same mixing bowl (no need to clean), beat the egg yolks and remaining sugar on high speed for 1 minute. Add the oil, milk, vanilla, and espresso powder, and beat for another 2 minutes until the mixture is thin and slightly bubbly.
Gently fold in the whipped egg whites in two additions, mixing on low speed for 10 seconds after each addition.
Sift in the flour mixture and fold the batter together with a silicone spatula until just combined. Do not over-mix.
Spread the batter evenly into the prepared pan, creating a thin layer. Shimmy the pan on the counter to smooth out the top.
Bake for 12-14 minutes, until the top of the cake lightly springs back when touched.
Prepare to Roll/Roll the Cake:
While the cake bakes, lay a piece of parchment paper or a thin kitchen towel larger than the cake on the counter. Dust it with about 2 tablespoons of cocoa powder.
Once the cake is done, quickly run a knife around the edges and immediately invert it onto the prepared parchment or towel. Peel off the parchment paper from the cake.
Starting with the narrow end, tightly roll the hot cake with the parchment/towel. Allow it to cool completely at room temperature while rolled, about 3 hours.
Make the Whipped Cream:
In a medium bowl, using a hand mixer or stand mixer with a whisk attachment, whip the cold heavy cream, sugar, and vanilla extract on medium-high speed until medium to stiff peaks form, about 2-3 minutes. If using, beat in the marshmallow creme.
Fill and Roll the Cake:
Slowly and gently unroll the cooled cake. Spread the whipped cream evenly over the surface, leaving a ½-inch border. Carefully roll the cake back up, this time without the parchment/towel. Place the roll on a wire rack set over a baking sheet to catch any ganache drips.
Make the Ganache Topping:
Place the chopped chocolate and corn syrup (if using) in a medium bowl. Heat the cream in a small saucepan until it begins to gently simmer. Pour the hot cream over the chocolate, letting it sit for 2-3 minutes to soften. Slowly stir until the chocolate is fully melted and the ganache is smooth and glossy.
Finish the Cake:
Pour the ganache over the rolled cake, allowing it to cover the cake evenly. Spoon any dripped ganache back over the cake if desired.
Refrigerate the cake for at least 30-60 minutes before slicing and serving.