Preheat oven to 180C. If you have a split oven use the large part and put rack in the lower 1/3 so that cake will bake in the middle of the oven
Make the coffe from the hot water and instant coffe. Leave to cool
Sift flour, cocoa, baking powder & baking soda together
Seperate eggs. Use a bowl with a sharp edge to help make the crack cleaner and the egg easier to seperate
Put egg whites into freezer until just starting to form ice (about 10 min)
Beat egg yolks (colour will change. Add half of the sugar and continue to beat until creamy pale
Add oil to yolks. Mix. Add coffee and vanilla. Mix
Mix wet into the dry ingredients gently. Avoid over mixing as this will form gluten and ruin the soft texture
Begin whipping egg whites on medium with an egg beater or cake mixer
When large bubbles begin to form add cream of tartar down the side of the bowl continuing to whip
When the bubbles become small, the white has foamed, and is roughly 4 times in size begin to slowly add the sugar down the side of the bowl continuing to whip. Be gentle so as not to collapse the bubbles
Once added turn the beater up to high and beat until the stiff peak stage is reached (peak stays formed when drawn up with only the very tip bending over)
Fold the egg whites into the batter piece by piece. Once complete they should be just mixed. It is okay if they seem slightly undermixed so long as there's no streaks
Bake 35-40 minutes until a skewer comes out clean. Then cool upside down on a wine bottle (if you have a bundt type pan) or on a cooling rack otherwise. This is so the cake doesn't shrink as the air trapped inside cools
Once completely cool (1-2 hours) it is safe to remove from the pan. The flavour and texture is best if left for at least 24 hours in an airtight container
Garnish by dusting with icing sugar if you so please and enjoy :D
Notes
You really want to be using a bundt pan/angel food pan for this cake (of heavy aluminum with a removable inner) and without greasing the pan. By sticking to the pan the cake can rise properly as it has a tendency to collapse under its own weight