So, the technical challenge for cake week on the Great British Bake Off was Gateau Vert – a green cake made green by pistachios and spinach. Now, it was Prue Leith’s choice and she chose it, so she said, because it was Claude Monet’s choice of birthday cake. I’ve never heard a more spurious reason for liking a cake. Come on Prue, even if you don’t really like gateau vert or, like most of us, had never heard of it before it was made into a Bake Off challenge, surely you can come up with a better reason than that. “I love pistachios,” would have done, or “green is my favourite colour”. Liking a cake because a famous artist liked it so much he had a couple of slices per year just doesn’t ring true.
Anyway, whether Prue Leith really likes gateau vert or not is beside the point. She set it as the technical challenge for cake week, and so I decided to give it a try. The recipe is available on The Great British Bake Off website but I needed extra help for the génoise sponge and the French butter cream. I turned to Edd Kimber and his Patisserie Made Simple for both.
Here’s how the cake turned out.
I certainly succeeded on making it green. How did it taste though and would I make it again? Let’s find out.
Step One: Pistachio Marzipan
The first step of the recipe was to make a pistachio paste to cover the cake before icing it. I needed 300g of pistachio kernels for this. Here was my dilemma. Did I buy ready-shelled pistachios or not? The ready-shelled nuts were, obviously, more expensive. There was no way of telling, however, what weight of pistachio kernels I’d get from a bag of unshelled pistachios. I went with unshelled. From a 200g bag of Tesco’s unshelled pistachios, I got 104g of pistachio kernels. I think, taking costs and the time it took to prise 300g worth of pistachio kernels out of their shells, buying the shelled version was a false economy.
Anyway, once I had my pistachio kernels, I ground them into a paste, mixed them with icing sugar and added an egg white. The recipe says that the egg white should be whisked, but no more than that. I wasn’t sure whether the egg white needed to be stiff, or just bubbly. Since I was using it to make a paste, I kept my egg white on the liquid side.
I was also supposed to add pistachio essence at this stage, but I couldn’t find any in Leamington and I didn’t fancy a trip anywhere else just for a bottle of flavouring. Given the amount of pistachios in the recipe, I couldn’t see why any extra pistachio flavour would be required.
I made the pistachio, sugar and egg white mixture into a paste, kneaded it for a couple of minutes, wrapped it in clingfilm and put it into the fridge.
Step Two: Génoise Sponge
The second step of the recipe was to make the cake itself. I ground another batch of pistachios and mixed them with plain flour. Separately, I mixed caster sugar and eggs in the KitchenAid. The recipe says that you should whisk the eggs until they are pale and thick, then fold in the flour, some melted butted and lemon zest.
I made a génoise sponge before, when I made a fraisier, and remembered that there was more to it than simply folding flour into eggs and sugar. I turned to Edd Kimber, whose recipe I used in the past. Sure enough, I was right.
To make a génoise sponge, you need to whisk the eggs and sugar for a really long time. Edd Kimber suggests eight minutes. Yes, the mixture does need to be pale and thick when you stop whisking, but it also has to leave trail on the surface that slowly dissolves into the mixture. Without Edd’s help on this I’m sure I’d have stopped whisking far too soon. When the eggs are whisked, you do fold in the flour, but you do it in stages. When you’ve folded the flour in, you do add melted butted as per the Great British Bake Off recipe, but, to do this, you mix the butter with a little bit of the egg mixture before you fold it in.
Once everything was folded in, I put the mixture into a deep cake tin and put it into the oven at 160° fan. It had 25 minutes in the oven (the recipe baking time was between 20 and 30 minutes). I left the cake in the tin for ten minutes, then turned it out onto a wire rack. It looked OK. It had risen nicely. I was definitely going to be able to make three layers out of it.
Step Three: French Buttercream
This is where the spinach came in. I added some spinach leaves to a pan of boiling water and let them wilt. The recipe says this should take 2-3 minutes, but my spinach only really took a few seconds to wilt. Definitely not more than a minute. I put the spinach and the water into my blender and blitzed it. This is what I ended up with. Nice.
I squeezed the spinach through a muslin square, and ended up with a bowl of green water. Even nicer.
Let’s get back to the buttercream itself. I ground yet another batch of pistachios and added a dash of kirsch, a tablespoonful of the lovely spinach water, and some butter. This made a green paste, which I set aside for later.
Next, I dissolved some caster sugar in more of the spinach water. In the meantime, I had the KitchenAid by the hob and started to whisk an egg yolk. Here I turned to Edd Kimber again because the Bake Off recipe wasn’t clear about how much the eggs needed to be whisked. According to Edd, they have to be whisked at high speed until they are pale and thick.
While the eggs were whisking, my sugar and spinach water started to boil. This was OK, because you have to boil the sugar to a certain temperature before adding it to the eggs. Again, I used the Edd Kimber recipe for this step. The sugar has to hit 120º before you pour it into the egg. I had the same problem measuring the temperature that I had last week when I made wagon wheels. I don’t think my sugar was quite there when I decided to pour, I was too worried about it burning.
Carefully, I poured the sugar and spinach water onto the egg mixture with the KitchenAid going at high speed. I whisked until the mixture was cold and then added diced, room temperature butter a couple of pieces at a time. My buttercream looked (and smelled) awful. I remembered that I was supposed to add the pistachio paste. Hopefully this would make things better. It did. Somehow, adding the paste turned my foul-smelling green splodge into a green buttercream that had nothing of the vegetable plot about it.
Step Four: Assembly
To put the cake together, I cut the sponge into three layers. They were a little bit uneven, but they’d do. I sandwiched the layers together with the butter cream, and covered the cake in a thin crumb-catcher layer.
To decorate the cake, I made fondant icing using icing sugar and the spinach water. Again, I should have added some pistachio essence, but had to leave this out since I didn’t have any. I put the cake onto a wire rack and the wire rack over a roasting tin. Then I poured the icing over the top and decorated the cake with some ground pistachios and flowers. I know the Bake Off contestants used some beautiful edible flowers on theirs. The only thing I could find in the garden was a soggy nasturtium, so I used some paper flowers left over from my daughter’s birthday cake.
Here’s my gateau vert, in all its greeness.
Was it Worth It?
The cake did look good, it’s true and, inside, it had nice, fairly even layers of buttercream and sponge. It really didn’t taste of much though. I know the pistachio essence was missing, but I thought that it wouldn’t matter too much because there were so many real pistachios in the cake. The marzipan was good, but, to be honest, the overriding taste from the cake came from the icing which was, mainly, sugar.
I also have to have a moan about the recipe. I know that, for a technical challenge, the Bake Off contestants aren’t given very many details, but if you’re publishing a recipe that you actually want people to bake, they have to have some idea of what to do. All in all, I’d say that this was a style over substance cake. No wonder Monet only wanted it once a year.