Preheat oven to 325F (160C) and line two 8-inch cake pans with parchment paper. You can grease the bottom, but do not grease the sides of the pans.
Measure the cocoa powder (90g) in a large bowl then pour over the hot coffee. Mix until smooth, set aside for five minutes then mix in the oil. Set aside.
Sift the cake flour (240g) 2-3 times and set it a side.
Whip the eggs (6) and sugar (350g) over high speed until tripled in volume, and you have a pale yellow mixture. This can take up to 10 minutes.
Sift the cake flour over the egg mixture in three additions, using a large whisk to fold the flour into the mixture.
Add about one cup of the egg mixture into the cocoa mixture and mix until smooth.
Pour about 1/3 of the cocoa mixture into the egg mixture and use a rubber spatula to fold it. Once it is mostly incorporated add another third, repeating with the rest of the cocoa mixture.
Divide the batter between the two pans and bake over the middle rack for 30-35 minutes. Do not open the oven door before the 25 minutes mark.
Remove from the oven and allow the cake to cool completely in the pans before inverting and filling.