Preheat oven to 180 degrees C (350 degrees F). Line two 18 cm (7 inch) cake pans with circles of baking paper. Grease very well inside the pans.
In a large mixing bowl combine sifted flour, sifted cocoa powder, baking soda, baking powder, cinnamon (optional) and sugar. Mix with a hand whisk to blend the ingredients.
In a separate bowl combine eggs, vanilla extract, olive oil and buttermilk. Whisk well until the mixture becomes smooth and uniform.
Pour the wet ingredients into the dry ones. Whisk gently, until combined.
At the end gradually pour the coffee (or water). Continue whisking carefully, until smooth. The batter should not be thick, neither too thin. If you see that the water is too much and will make the batter liquid, don’t use the whole quantity.
Transfer the batter into the prepared pans dividing it in relatively equal parts.
Bake for 40-50 minutes or until a toothpick inserted in the centre of each cake comes out clean.
Let the cakes cool for 5-10 minutes and then remove them from the pans: carefully run a knife around the edges, then hold the pan with kitchen gloves and invert on top of a wire rack or wooden board.