Preheat the oven to 190 C / 170 C fan / Gas 5. Grease and line two 20cm sandwich tins.
Put the butter and sugar into a bowl and mix until creamy and lighter in colour, using a spoon, hand held mixer or free-standing mixer.
Sift the cocoa, flour and salt into a bowl and crack one of the eggs into a cup or ramekin. Stirring all the time, add the egg and a third of the flour mixture into the sugar and butter, add the second egg and third of the flour and add the last egg and flour mixture in to the butter and sugar. You should have a smooth thick batter. If your batter is stiff, add a splash of milk and stir. Put even amounts of the mixture into the tins and spread using a knife.
Bake in the preheated oven for 25 minutes until springy to touch. Take out of the oven at leave them in their tins for 10 minutes before turning out onto a wire rack to cool completely.
Look at my recipe for buttercream icing so you can decorate your cake once its cooled down! :)