Dome cake made from the lightest sponge, filled with layers of dark chocolate, raspberry mousse and vanilla buttercream, glazed with white chocolate ganache. The ultimate in ‘wow’ factor.
Dome cake is not your weekend bake – it’s a project. It will easily take up to three days, several bowls, buckets of cream and a bit of skill. But it’s THE cake to prepare for a special occasion, birthday or anniversary, when you want something outstandingly different and overwhelmingly indulgent.
My dome cake was inspired by a wondrous dessert I was once served in a French restaurant. An individual half-sphere covered with white chocolate, hiding lovely raspberry mousse and delicate sponge inside. It came from a dessert trolley that had no labels, and it (rather stupidly) didn’t occur to me to ask what it was called.
It was ridiculously delightful, and it got me thinking of a full-sized cake in the shape of a dome. So I went back home and started experimenting.
How to make a dome cake?
Baking the sponge in a special, half-sphere-shaped tin would be the immediate solution but a/ such tins are hard to come by, and b/ I hated the thought of using a tin just the once and have it knocking about the cupboards purposelessly ever after. And it would be a solid half-globe as well.
But sponge, as the name suggests, is reasonably pliable so shaping it to a required silhouette should not be a huge problem.
And it wasn’t. So here’s all you need to know about the elements of this impressive gateau. And in fact each of them: the sponge, the chocolate mousse, the raspberry filling, the buttercream and the white chocolate glaze is a separate recipe, well worth noting and using in a simpler production.
The dome cake sponge
The sponge is the skeleton: the outer and bottom layers and a thin one in the middle, the latter possible to be skipped if the fuss becomes too much.
But an ordinary, English, Delia-style sponge won’t do here. The cake would be far too heavy.
Genoise is just the thing: it is the lightest, fluffiest and airiest type of sponge, but keeping its shape when moulded and filled. It’s quite a work of art, but if you follow the recipe, it unfailingly succeeds.
No egg separating, but the eggs must be beaten to five times the volume! To facilitate this, start off over a pan of simmering water, aka bain-marie. When they reach body temperature – importantly, they must start off at room temperature, otherwise you never get there – take them off the double boiler and whisk them to oblivion.
The little flour that goes in there must be perfectly sifted – don’t skip that step. Fold it super-gently, and then just a little melted butter is added, to give the batter stability.
After it’s baked, the fun part: drop the cake from a height onto folded towels. It helps distribute the air bubbles in the sponge and, counterintuitively, stops it from sinking. Turn it upside down, then right side up and it’s ready to unmould and cool.
How to cut sponge into layers
A wire cutter for cakes is a nifty tool, but if you haven’t got one, there are some hacks. A super-steady hand armed with a super-sharp bread knife might do it just like that, but you only get one go at it, and bread knives are never sharp.
Mark the layers on the side of the sponge and use a length of cotton thread to wrap around it where you want to cut. Twist the thread as if you wanted to strangle the cake until it cuts through.
How to make chocolate mousse frosting
This chocolate frosting is one of the easiest: it is nothing but a whipped chocolate ganache. Stick to the correct proportions of chocolate to cream and don’t over-whip. That’s all.
It can be made with milk or white chocolate too (without the sugar) for another occasion. Indeed it is delicious on its own, served as a mousse for dessert.
How to make raspberry filling for cake
This is an excellent filling that keeps its shape, isn’t too sweet and needs no gelatine. It is simply raspberries cooked down with sugar, pureed and thickened with some corn flour.
If you don’t think raspberry seeds are going to cause anyone problems, you can even skip the pureeing process. In fact, the filling will set quicker and better with the seeds in.
It’s great to use in cakes as filling and will make a nice contrast with buttercream, being also lighter and tangier than jam. But it’s absolutely fantastic as pastry filling: Danish, tarts and tartlets because it can be baked with the pastry.
The easiest buttercream
I have made some gorgeous Swiss meringue buttercreams, but the dome cake is a massive venture so I want to cut a few corners where possible. And there’s nothing wrong with the simplest vanilla buttercream, the better for it if you can use real vanilla pods.
Just remember to start with soft butter and beat it into feathered peaks. The amount of sugar must be nearly twice as much as butter, or it will taste like butter. And a little cream added at the end makes it lighter.
Step by step: how to build the dome cake?
A bowl, the size of the baked sponge or bigger, lined with cling film, will be the mould. Once the sponge is cut into layers, press one into the bowl cut side up.
The dark chocolate mousse will go onto the sponge in not too thick a layer, just so we manage to fit all the fillings into the dome. If time allows, chill it to set before spreading the raspberry filling next, up to just below the edge.
Next comes the thinnest, middle layer of the sponge, trimmed to size.
Follow that with buttercream, piped in or just spooned. It's best to work with it at room temperature. The final sponge layer will come on top, which will afterwards be the bottom. Complicated? Not at all.
The assembled dome must now chill and set in the fridge, for at least an hour and overnight if possible.
And now the big moment: turning the cake out! Gently, onto a cake base, peeling the cling film off carefully if it stuck a little.
And onto the final touch - glazing the dome with white chocolate ganache.
White chocolate ganache frosting
Ganache is the loveliest frosting: it always looks and tastes good. And who doesn’t like creamy chocolate on a cake?
For spreading over the finished dome, as opposed to the whipped dark chocolate mousse that went inside, the ganache must be thick: a lot of chocolate and only a little cream. The addition of a small knob of butter will make it glossier.
It sets fast so needs to be used immediately after mixed.
And there we have it! One dome cake. It might not be as perfect as those sky-high painted works of art that my talented neighbour makes, but it is accomplishable for a less artistic cook and baker, like me. Or perhaps you?