The combination of cocoa plus melted dark chocolate gives this cake very rich flavour and texture and it keeps soft for days. The olive oil flavour is clear but subtle, but you can replace it with any vegetable oil for a more regular flavour. Ditto the coffee; for children you might want to try using warm milk or fruit juice instead.
300g dark muscovado or brown sugar
350ml milk (for dairy-free, see tips in method)
2 eggs, 60g each
100ml extra virgin olive oil
100g dark (70 per cent) chocolate, melted
250g plain flour
75g cocoa powder
1 tsp baking powder
½ tsp bicarbonate of soda
100ml hot black regular coffee, not espresso-strength
For white chocolate mascarpone buttercream
250g unsalted butter, soft at room temperature
250g icing sugar
200g white chocolate, melted
For the cake
1. Line the base of two deep round 20-centimetre sponge tins (not the removable base kind as the cake batter is quite liquid) with non-stick paper, and heat the oven to 180C (160C fan forced).
2. Put the sugar in a bowl and whisk in the milk. Whisk in the eggs then the oil and melted chocolate.
3. Sift in the flour, cocoa, baking powder and bicarbonate, whisk until smooth then beat in the coffee. The mixture will be very liquid, thick soup consistency, but don't worry. Pour it evenly into the tins and bake for about 45 minutes or until a skewer poked in the centre comes out clean.
For the buttercream
1. Beat the butter with the icing sugar until smooth. Add the mascarpone and beat until just combined, no more. Then add the melted white chocolate and beat again until just combined and fluffy.
2. Spread half of this over the top of one cake, sit the other cake on it, then finish with the remaining icing though you will have a some left over. Stores well covered in the fridge, bring to room temperature and gently beat again until smooth to use.
Tips: The cake can be made dairy-free easily, by replacing the milk with almond milk or juice, and decorating with a simple chocolate icing.
The buttercream is utterly extravagant, and perfect for a bittersweet chocolate cake. The trick to keeping the texture light is to avoid overbeating it. Makes more than you need to cover and sandwich a 20-centimetre round cake thickly.