Pre-heat oven to 180C / 350F
Grease a 9" cake pan with oil and set aside
Mix together the dry ingredients - flour, cocoa, salt, baking powder, baking soda, coffee powder, and sugar until well combined
Add oil, egg, vanilla, and milk to this and stir well to combine without any lumps
Add boiling water to this batter and mix well
The batter will be very runny and this is perfect
Pour into the baking pan and bake in pre-heated oven for 30-35 minutes
Let cool completely before frosting as needed