- Preheat the oven to 180°C/160°C (fan)/gas mark 4. Grease and line a 15cm round cake tin. 
- Whisk together the butter, caster sugar, and brown sugar until light and fluffy. 
- Whisk in the eggs one at a time and add the vanilla extract. 
- Fold in the cream and flour gradually, alternating between the two (a splash of cream, then a spoonful of flour, and repeat). 
- Fold in the black cocoa powder, milk, and salt. Transfer the batter to the prepared cake tin. 
- Bake for 45-60 minutes, or until a skewer inserted into the center comes out clean. 
- Leave the cake to cool in the tin for 10 minutes, then transfer it to a wire rack to cool completely. 
- For the frosting, beat together the butter, icing sugar, cream cheese, and vanilla extract for 2-3 minutes until smooth. If not thick enough, add more icing sugar as needed. 
- Once the cake is completely cool, divide it into layers and fill with the frosting. Decorate with sprinkles if desired and serve.