Step 6:
Evenly distribute the batter into the prepared pan. The coating will be quite thin. Move the pan on the counter to even out the surface. Bake for 10 minutes, or until the cake’s surface softly bounces back when lightly touched. Do NOT over-bake.
Step 7:
While the cake is baking, lay a piece of parchment paper (bigger than the cake) or a thin kitchen or tea towel on the surface.
Step 8:
Using a fine mesh sieve, sprinkle 2 Tablespoons of cocoa powder over the parchment/towel. Quickly release the cake’s edges with a knife after removing it from the oven. Invert it immediately onto the cloth or paper.
Step 9:
Remove the baking-time parchment paper from the bottom of the cake. Beginning with the narrow end, firmly roll the hot cake in the parchment/towel. Do this slowly and softly. Warm will be the cake.
Step 10:
Let the cake cool fully while rolled in the towel/parchment. You are free to refrigerate it to hasten the process, about 3 hours to 1 day. If the cake was refrigerated, it should be brought to room temperature. If unrolled when cold, the cake is likely to split.
Step 11:
Using a hand mixer or stand mixer equipped with a whisk attachment, beat the heavy cream, sugar, and vanilla extract on medium-high speed until medium to firm peaks form, about 2 to 3 minutes. Next, if using, beat in the marshmallow cream.
Step 12:
Unroll the cake delicately and slowly. Pour whipped cream on top of the cake evenly, leaving a 1/2-inch border around the edge. This time, without the towel or paper, roll the cake back up gently. Place on a wire rack positioned atop a baking sheet (to catch the extra ganache). Place on the counter or in the refrigerator while you create the ganache.
Step 13:
Prepare the ganache topping by combining, in a medium bowl, chopped chocolate and, if using, corn syrup. In a small saucepan, bring the cream to a boil before serving. Pour over the chocolate, then let it settle for 2 to 3 minutes to soften the chocolate. Stir slowly until the chocolate has melted and the mixture is well mixed.
Step 14:
Cover the whole cake roll with ganache. If any ganache drips onto the cake, feel free to scoop it up and drizzle it back on top. Before slicing and serving, refrigerate for at least 30 to 60 minutes.