Hello! How far ahead can I put the topping on Nigella's Nutella Cake, and can I make the topping beforehand and put it on before serving the cake? Thanks.
The topping for Nigella's Nutella Cake (from Domestic Goddess) is a combination of a chocolate ganache icing and whole skinned and toasted hazelnuts. The hazelnuts can be toasted up to a week in advance. Let them cool completely and then store them in an airtight container in a cool place until needed.
The ganache icing, a mixture of melted chocolate and cream, can also be made up to a week ahead, then transferred to a heatproof bowl, covered with clingfilm (plastic wrap) and refrigerated until needed. However you will need to very gently and carefully re-warm the icing to a pouring consistency - either by setting the bowl over a saucepan of warm water or with short bursts in the microwave - and it is actually easier just to make the icing when you need it.
You will probably find it easiest to ice the cake and put the hazelnut topping on 3-4 hours before serving, thiough you could ice and add the nuts the night before if you have a large cake dome that can cover the whole cake.
If you can only find hazelnuts with their skins on then you could instead toast the hazelnuts in the oven and then remove the skins. To do this, toast the nuts in an oven preheated to 180c/350F for 10-15 minutes, until they look like they have turned slightly golden underneath and smell slightly toasty. Carefully transfer the nuts to a clean and slightly dampened tea towel (dish cloth) and rub until most of the skins have been removed. Let the nuts cool completely before using them on the cake.