Green Monet Cake Adventure Part Two

“I thought he was joking.”

But Noel Fielding isn’t kidding when he tells the Great British Bake-Off contestants that they’re making a Monet cake colored green with spinach for their technical challenge. Welshman Jon Jenkins expressed disbelief at first, but he’s got some tricks up his sleeve.

I lost count of how many times I watched that video, trying to figure out what to do.

Prue Leith’s version of Claude Monet’s birthday favorite gâteau vert is so maddening that I wondered whether she’d taken a reasonable cake recipe and made it harder just for the show. Sadly, no. From my research, her biggest change was adding the pistachio marzipan. Blanching and peeling pistachios is so tedious (yet necessary) that I felt fine about skipping it.

Prue’s original inspiration probably came from a cookbook. Several feature Monet’s “vert-vert” cake alongside reproductions of his paintings and other recipes he liked. Narrowly avoiding a book-buying binge, I thought this one seemed close. An archived French recipe presented a cake with three layers, but they’re super thin. I’ll stick to two. While the roses on top are gorgeous, using spinach water rather than strained purée produced a paler green.

What’s so hard about this green cake? The genoise sponge, as I already discovered. Then the French buttercream, which involves whipping fresh raw egg yolks and — my nemesis at altitude — homemade boiled syrup. Culinary folks warn that this buttercream can split if the temperatures aren’t just right. And let’s not forget about the green icing at the end.

I’m calling it “icing” instead of the confusing “fondant icing.” The ingredients are similar to a successful icing from the “Hand-Forged Doughnuts” cookbook. Only instead of warm water, I’d use spinach water — and a bit of historically inaccurate corn syrup for a nicer finish.

Slightly before 5 o’clock on a Monday I got to work. The genoise inexplicably cratered in the middle. I read the recipe too fast and didn’t grind the pistachios before adding the rest of the paste ingredients. Guillaume helped me with the syrup because I feared it would turn into a ball of spinach candy. The icing didn’t pour so much as ooze.

None of that mattered once I arranged the edible flowers on top, including some late-season borage. The time? About 7:20 pm. Not bad at all. For pistachio lovers like ourselves, the cake was a tasty treat. I can see why Monet wanted it on his birthday.

Monet’s Vert-Vert Cake

Genoise Sponge:
25g unsalted butter plus more for greasing pan, at room temperature
50g raw pistachio kernels, blanched and peeled
75g all-purpose flour
125g caster sugar
Pinch of salt
4 large eggs, at room temperature
Grated zest of 1 lemon (about 1 tsp.)

French Buttercream:
300g spinach (about 10 oz.)
100g pistachio kernels, blanched and peeled
1 Tbsp. kirsch
150g unsalted butter, softened but slightly cooler than room temp
80g caster sugar
2 large egg yolks, at room temperature

Icing:
250g powdered sugar
3 – 4 Tbsp. spinach water
½ tsp. almond extract
¾ tsp. light corn syrup
Pinch of salt

Decoration:
25g pistachio kernels, blanched and peeled
Edible flowers

Special equipment: 9-inch round cake pan, a piece of cheesecloth, cake lifter, blender or food processor, a stand mixer with whisk and paddle attachments, digital scale.

Genoise Sponge:
Grease a 9-inch round cake pan with unsalted butter and line the base with parchment paper.

Preheat the oven to 350°F.

Melt 25g unsalted butter. Zest the lemon and mix it into the butter. Add a pinch of table salt. Set aside.

Finely grind 50g of raw peeled pistachio kernels in a food processor. Then add the 75g of flour and grind that together for a little longer until combined. Remove to a bowl and mix with a fork.

Place the eggs and caster sugar in the bowl of a stand mixer with the whisk attachment. Whisk on low for 1 minute. Switch to medium-high and whisk for around 10 minutes or until the eggs are pale, extremely thick, and tripled in volume. Be patient. The volume can only be lost from here.

Add about a spatula-full of the batter to the bowl with the melted butter and mix it together gently until uniform in texture. This makes the butter easier to incorporate later. Set aside.

Sprinkle about one third of the flour mixture over the top of the big bowl of batter, and fold it in very gently, leaving some streaks. Then do the same with another third of the flour, and then the rest. Now fold the buttery-batter in gently.

Getting the bowl as close as possible to the prepared cake pan, carefully pour the batter into it, using the spatula as a guide. You don’t want to lose any precious volume.

Bake for 20 minutes or so, until risen and springy to the touch. Check for doneness with a toothpick. Set aside to cool for 5 to 10 minutes, then turn out onto a wire rack set in a baking sheet to cool completely.

Move the cake to a large cutting board with a cake lifter. Slice the cooled sponge carefully into two thin layers. Put the sliced cake aside and keep the wire rack in the baking sheet handy for icing later. Clean and dry the stand mixer bowl and attachment.

French Buttercream:
Boil 150ml water in a large pot. Add the spinach, turn down the heat to medium-high, and wilt for 2 to 3 minutes, stirring occasionally. Transfer the spinach to a blender using tongs, add a couple tablespoons of the remaining water, and leave the rest of the water in the pot just in case. Blitz the spinach to a purée.

Set a single layer of cheesecloth over a bowl or large glass measuring cup. Add the purée, pull up the sides of the cheesecloth, and carefully squeeze out as much of the spinach water as you can. You should have around 160 to 170ml. Set the spinach water aside.

Put 100g pistachios in a small food processor (or blender) and grind as finely as possible. Now add 1 tablespoon of kirsch, 1 tablespoon of the spinach water, and 50g of the softened butter. Blitz to a pistachio paste and set aside. It doesn’t have to be completely smooth.

Whisk 2 egg yolks in a stand mixer with the whisk attachment until pale and thick, about 6 to 8 minutes. Scrape down the sides periodically.

Put 80g caster sugar and 100ml of the spinach water in a small pan, reserving the remainder of the spinach water. Dissolve the sugar gently over low heat, and then boil for on medium until the syrup thickens and starts to forms a thread when pulled between two spoons.

Slowly add the syrup to the yolks in a thin stream down the side of the bowl while whisking on low. Stop pouring every 10 seconds or so and increase the speed to high, then switch back to low and drizzle in more syrup. Continue until all the syrup is incorporated. Scrape down the sides of the bowl.

Once the syrup is added, whisk on high speed until the mixture is thick and cold, which could take about 10 minutes. After the bowl is cool to the touch, switch to the paddle attachment. Going a tablespoon at a time, add 100g of the softened butter, mixing well before adding the next piece. Finally, add the prepared pistachio paste and mix on medium speed until the buttercream is smooth and creamy. (Here are tips on what to do if it breaks.)

Using the cake lifter, remove the top layer of sponge and set it aside. Spread a thin coating of buttercream over the bottom cake layer with a large flexible spatula. Put the top layer of sponge back on. Spread the rest of the buttercream over the top and sides of the cake. Move the cake back to the wire rack set inside a baking sheet.

Icing and Decoration:
Sift 250g powdered sugar into the bowl of a stand mixer with a paddle attachment. Add a pinch of salt, ½ teaspoon of almond extract, and ¾ teaspoon of light corn syrup. Now add 3 tablespoons of the spinach water. Blend on low speed until smooth and all of the powdered sugar has been incorporated, scraping the sides with a spatula as needed.

Slowly more spinach water a teaspoon at a time until the consistency is smooth and pourable. Pour the icing evenly over the cake. Allow it to drip for several minutes, then use a cake lifter to transfer it to a cake plate or stand.

Roughly chop the remaining 25g pistachios and press them around the base of the cake, then arrange edible flowers on top to serve. To store leftovers, remove any flowers from the top prior to refrigerating.