Preheat oven to 160°C Fan/180°C conventional/ 350°F. Grease and line the base and sides of 2X 8 - inch round cake tin with greaseproof paper.
In the bowl of your stand mixer sift together cocoa powder, sugar, flour, bicarbonate of soda, baking powder and salt.
In a measuring jug or bowl combine eggs, oil, milk, and vanilla extract. Add liquid mixture to flour mixture and beat on medium speed until smooth and incorporated. Stir in hot water.
Divide chocolate cake batter equally between the cake tins.
Bake for 30 minutes or until a toothpick inserted in the centre comes.
Leave the cake to cool in the tin for 10 minutes. Invert onto rack gently, discard parchment paper and then cool completely.
Wrap in cling film and chill in fridge until ready to use.