Start by preheating your oven to 350°F. Lightly grease the bottom and sides of a baking sheet or jelly roll pan with cooking spray or melted butter. Line it with parchment paper and lightly spray the paper as well. This prevents the sponge cake from sticking and ensures a smooth release.

In a large bowl, use an electric stand mixer with a whisk attachment or a hand mixer to beat the eggs on medium-high speed for about 3 minutes until frothy and pale. Gradually add sugar and continue beating for 4-5 more minutes. The mixture should triple in volume, becoming thick, fluffy, and billowy like shaving cream or marshmallow fluff. When lifted with a beater, the mixture should fall back in folds or ribbons rather than sinking immediately.

Add vanilla extract and salt, then slowly drizzle in oil while mixing. Ensure everything is incorporated well without overmixing.

Sift together flour, cocoa powder, and baking powder into a medium bowl and whisk them to blend evenly. Sift the dry ingredients again over the egg mixture and use a rubber spatula to gently fold them in two stages. Ensure there are no streaks of flour left but avoid over-mixing, which can deflate the batter.

Carefully spread the batter in an even, thin layer on the prepared baking sheet using an offset spatula. Bake for 9-11 minutes, or until the cake springs back when pressed gently. Be careful not to overbake, as it can dry out the surface.

Roll and Cool the Cake

Transfer the pan to a wire rack and let it cool for a minute. Lightly dust the cake with icing sugar or cocoa powder. Run a knife along the edges to release it, then carefully invert onto a clean kitchen towel or another parchment sheet. Gently peel off the top layer of parchment. While still warm, roll the cake into a tight log starting from the short side, incorporating the kitchen towel or parchment in the process. Let it cool completely in this rolled shape with the seam side down.

To make a chocolate ganache, heat ⅓ cup (80ml) whipping cream in a saucepan over medium heat until it starts to simmer. Remove from heat and add chopped dark chocolate. Let it sit for a minute, then whisk until smooth and glossy. Let it cool for 5 minutes. In a separate bowl, beat ¾ cup (180ml) whipping cream until it forms firm peaks, then gently fold in the cooled ganache.

Carefully unroll the cooled cake and spread the chocolate filling evenly, leaving about a ½-inch border around the edges. Apply a bit more filling to the end that will form the center of the spiral for a well-defined shape. Roll up the cake again, then transfer it to a serving plate or baking sheet. Cover it with plastic wrap and refrigerate for at least 2 hours to set. Before serving, dust with cocoa powder for a beautiful finish.