Combine all the powders (flour, sugar, cocoa, baking powder and bicarbonate of soda) in a bowl and mix, then also add the liquid ingredients (eggs, vanilla, sour cream, soft butter at room temperature) and mix.
Pour into the buttered and floured mould, level the surface with a spatula and cook for around 40-45 minutes at 180°C, in a pre-heated static oven (be sure to always do the toothpick test), then remove from the oven and leave to cool completely.
When the base is cold, prepare the cream: combine butter and chocolate pieces in a bowl and melt them (in the microwave or in a bain-marie), then leave them to cool.
Then add sour cream, golden syrup (or honey) and vanilla; once blended, add the sifted icing sugar, mixing until you obtain a uniform mixture.
(If you think the cream is too thick, add 1 tablespoon of hot water, if it seems too liquid, add 1 more tablespoon of icing sugar.)
Gently turn out the cake and cut it in half, then fill with 1/3 of the cream.
Close with the second disc, cover with the remaining cream and decorate as desired with chocolate chips.
Nigella’s chocolate cake is ready, all you have to do is enjoy it.