To make the batter: Separate the egg yolks from the egg whites. Set aside. (TIP: Cold eggs separate easily. See note 1 for more details.)
Preheat the oven to 350°F (175°C). Line a baker’s half baking sheet with parchment paper.
In a small bowl, sift together flour, cocoa powder, baking powder, baking soda and salt.
In a mixing bowl with a whisk attachment, whisk the egg yolks, ¼ cup sugar, vegetable oil, and coffee until tripled in size.
In another mixing bowl with a whisk attachment, beat the egg whites on medium speed until frothy.
Then add remaining ¼ cup of sugar, one tablespoon at a time. Increase the speed to medium high and continue to beat until soft peaks form.
Spoon half of the whipped egg whites into the egg yolk mixture. Mix with a spatula until smooth, and then add the remaining whipped egg whites. Carefully fold the batter until smooth.
Add the sifted flour mixture into the batter and gently fold until no dry flour is visible.
To bake: Pour the batter into the prepared baking sheet then smooth the surface evenly with a bench scraper.
Bake the cake for about 10 minutes, or until inserted toothpick comes out clean.
Cool the cake on a wire rack for 5-10 minutes. Run a flat spatula or butter knife along the edges. Using a fine mesh sieve, dust cocoa powder on top of the cake and place a piece of parchment paper on top. Then carefully flip the cake out onto a clean surface. (TIP: I place a large cutting board on top of the sheet pan and flip it over.) Peel off the parchment paper and cool the cake completely.