- With the rack in the middle position, preheat the oven to 180 °C (350 °F). Line two baking sheets with parchment paper and butter generously.
- In a bowl, combine the flour, cocoa powder, and baking soda. Set aside.
- In a large bowl, beat the eggs, egg yolks, and sugar with an electric mixer until light, tripled in volume and form a ribbon when the beater is lifted, about 10 to 15 minutes. At medium speed, drizzle in the oil, vinegar, and food colouring.
- Sift the dry ingredients over the egg mixture and fold gently, using a whisk. Spread evenly on the baking sheets. Bake for 12 to 15 minutes or until a toothpick inserted in the centre of the cake comes out clean. Let cool for 5 minutes. Invert the cakes onto parchment paper. Cover with a clean cloth and let cool completely.
- In a saucepan, bring the water, sugar, and corn syrup to a boil. Boil until a candy thermometer reads 113 °C (235 °F). Remove from the heat while whipping the egg whites.
- In a bowl, beat the egg whites with electric mixer until soft peaks form. Gradually drizzle the boiling syrup into the egg whites. The egg whites will swell and be steaming hot. Continue to beat for 10 to 15 minutes until stiff peaks form.
- Remove the paper from the top of each cake and place them side-by-side lengthwise. Spread evenly a quarter of the meringue. Roll the first cake and continue onto the second cake to form a huge log. With two large spatulas, place the log onto a large serving platter. Top with the remaining meringue. Store covered at room temperature. Serve the same day.
The recipe can easily be split in half into a log for 8 to 10 people. You then bake only one cake on one baking sheet.
If you prepare the cakes the day before, flip the cakes onto parchment paper. Remove the top paper. Roll the cakes, while still warm, with the paper from the wider side (for the bigger log) or the shorter side (for the regular-sized log). Let cool and wrap well in plastic wrap.