A genoise sponge is a perfect vehicle for all manner of gooey, luscious fillings. In fact the cake demands to be slathered in decadence as it is a light dry thing on its own, full of air and delicacy. You can bake this cake in two sandwich tins or make a Yule log by baking it in a Swiss roll tin. For a Yule log, I tend to bake mine in a large Swiss roll tin and then bake some in a smaller square tin so I can have a branch on my stump. Cooking time for a Swiss roll will be shorter, probably about 15-18 minutes - depending on how thick you made it. As with any recipe, just keep checking - but don’t go opening the oven door too early lest your cake fall in the chill draft. If you don’t have real coffee or a coffee grinder then you can use instant espresso powder - not quite the same flavour though, or leave out and make the chocolate version.
The butter ganache is essentially a ganache with lots of butter melted into it that can be whipped up like the most luxurious buttercream ever, or left as a fudgy milk chocolate ganache. The key to getting this right is patience - if it senses that you’re impatient it will split, just like your cat when you even think about taking it to the vet.
For a dairy free version, try using Coyo yogurt or chilled and whipped coconut cream for the filling and my dairy free ganache (below) for the coating - it’s not as soft as the butter ganache, but still very delicious. You can also make a beautiful frosting with a buttercream texture from blitzed avocado and melted chocolate or cocoa and maple syrup - not seasonal, but hey it’s Christmas!
I often add a crown of cookie shards, or chocolate bark shards with some piped butter ganache stars, and maybe a handful of toasted hazelnuts although chocolate curls are also cake shop perfect.
Coffee genoise
60g unsalted butter (or 50g coconut oil or cocoa butter)
6 large eggs (330g out of the shell) room temperature
200g caster sugar
160g buckwheat flour (or 100g buckwheat plus 60g cocoa for a chocolate version)
1 tablespoon real coffee blitzed in a coffee grinder with 1 tablespoon of caster sugar (optional)
Line two 23cm sandwich tins with parchment and preheat the oven to 175ºC
Melt the butter and set aside. Set up a Bain Marie over a gentle flame and stir the eggs and caster sugar with a balloon whisk until they warm up a little - but don’t over heat or they will scramble. Tip egg mixture into a stand mixer with a whisk attachment and whip on high speed for about 5-6 minutes until tripled in volume and the mixture leaves a rope that doesn’t dissolve into the rest. Scrape the meringue into a wider bowl for folding. Fold the flour into the fluff a third at a time, sifting it over the whole surface and then folding to avoid the meringue falling.
Warm the butter a little and scoop a few spoonfuls of meringue into the butter, beat until completely emulsified and then pour the buttery batter carefully over the meringue mixture. Fold until just incorporated, keeping the meringue batter light and airy.
Divide between the two tins and bake for about 20 minutes until the cake has risen and settled and a cake tester comes out clean. Cool completely in the tins and then unmould and slice each cake in half so that you have four layers.
Brush each layer generously with coffee syrup (recipe below) and sandwich with vanilla mascarpone cream. If you’ve made the chocolate version, for this I like to go Black Forrest and cook up some frozen black cherries, add a bit of bourbon, use the juice from this to brush the cake and add the cherries in the layers. Cover with a crumb coat of the butter ganache, chill and finish the cake with a top coat of ganache once it has thickened - or whip the ganache with a balloon whisk until it goes light and fluffy - like the most deliciously smooth and rich chocolate butter cream you ever ate.
Coffee Syrup
make a teacup of strong coffee and sweeten it to taste. Bring to a simmer and stir just until the sugar has dissolved. Add some Kahlua if you like. Cool and use as directed above.
Mascarpone cream
2-3 tablespoons of icing sugar
300g double cream
200g mascarpone
2 tsp vanilla extract or hazelnut/coffee liqueur
Dissolve the sugar in the cream, add the mascarpone and vanilla/liqueur and beat with a balloon whisk until smooth and thick. Use as directed above.
Butter ganache
150g milk chocolate - finely chopped
50g dark chocolate - finely chopped
160g double cream
pinch of sea salt
85g softened unsalted butter
In a bain marie, very gently melt the chocolate and cream together with a pinch of salt. Avoid stirring until everything is completely melted, just push the chocolate down under the surface of the cream. When melted, stir the mixture with a folding motion until everything is smooth. Put the bowl back over the Bain Marie - you may not even need to turn on the heat - and add the butter. Push the butter under the surface of the chocolate and leave to melt. When completely melted, use he same folding motion to gently stir until everything is smooth and glossy. Be patient - ganache this rich needs a touch of zen. Use the ganache as it is to spread a very thin ( and ugly) crumb coat on the filled cake, chill for 10-15 minutes until set and then cover with whipped or unwhipped ganache when the ganache has cooled and started to set a bit (put a piece of lightly buttered parchment on top while it cools). If you are whipping it, do this just before you use it, or it will sieze and become unspreadable.
Dairy free ganache
I give slightly less of this as it is not as good for piping, so this is just enough to cover the cake.
200g plain chocolate (50-55% cocoa solids, no higher) finely chopped
150g coconut cream
1 tablespoon coconut oil
Put everything into a bain marie and allow to gently melt, pushing the chocolate under the surface of the coconut cream, but not stirring. When everything is melted, use a folding motion to bring the ganache together, stirring gently until it is completely smooth. Allow to cool to room temperature and use to crumb coat the cake, then either allow to cool until it is thicker (takes much longer than cream ganache) or cheat by putting it into the fridge for a few minutes, stirring and repeating until it is the texture you want. Don’t leave in the fridge or it will go solid. If you like, you can whip it until it becomes thicker for a truffle frosting. Do this just before you plan to use it or it will seize and become unspreadable.