Beat the butter and sugar until fluffy and add the eggs 1 by 1, beating well after each. Sift the flour and baking powder together and add them to the mixture, this time beating only until they're mixed. Put the mixture in an oven dish with baking paper and bake at 356°F (180 °C) until the layer is ready. Leave the layer to cool completely and cut it in 2.
Leave the butter to soften and beat until fluffy. Then add the powdered sugar, whip until mixed, add the cocoa and beat until fluffy.
Heat the water in a pot on the stove until it simmers and add the sugar. Stir until the sugar dissolves and remove from the stove. Leave it to cool a little but it needs to be warm when using it or the cake layer will become soggy.
Place the 1st cake layer in the cake form and syrup it with the warm syrup. Leave the syrup to soak in for a few min. and evenly spread about half the buttercream on top. Place the 2nd cake layer on top, syrup once again, leave the syrup to soak in for a few min. Then smear the rest of the cream all over the cake and decorate with cinnamon sticks on top. Leave in the fridge for a few hours for the cream to solidify.