Pastry chef Rebecca Isbell does double duty at Italienne, the French-Italian Flatiron restaurant helmed by chef Jared Sippel. At night, she works behind a pristine marble pastry counter at the back of the dining room, plating elegant riffs on classic desserts for the fourth course of the restaurant’s $98 prix fixe menu. (Currently: a wild strawberry charlotte, a cascara tiramisu, and others.)
During the day, her prep work also includes production of simpler — though no less elegant — pastries for the more casual taverna, which occupies the front half of the restaurant.
Among these taverna pastries, which Italienne recently started offering not just as after-dinner desserts but also as anytime snacks from a takeout pastry counter, is the gateau au citron. Based on the gateau Basque, a rustic French cake baked with a filling of either custard or cherry jam, Isbell’s gateau looks a little plain. It’s a squat cake, two inches tall at most, coated in a basic glaze and served by the wedge without flourish.
But it is wonderful. It’s like a butter cake and a pie merged, creating, depending on how you look at it, either a dense cake with an exceptionally bountiful filling or a tart with an exceptionally thick, tender crust. Isbell adds poppy seeds to the cake, giving it the pleasant crackle of a lemon poppy seed loaf, and swaps out mild custard for a tart citrus curd, using whatever citrus is available — lemons, grapefruits, oranges, even pomelos — to lend a depth of flavor and fragrance beyond a standard lemon meringue. The result is surprisingly delicate, bright, and juicy for such a sturdy-looking slice.
Isbell plans to change gateau flavors with the season, so citrus and poppy seed may soon give way to rhubarb, but the formula — the ratio of thick fruit filling to buttery, cake-y crust — will never change. Read on to learn how Isbell makes her gateau au citron.
She starts by making the crust — with a recipe that yields something more like cookie dough than like cake batter or pie crust. After beating butter and sugar into a soft, creamy paste, Isbell adds a combination of whole eggs and egg yolks. “It’s a rich dough,” she explains as the mixer works the eggs into the butter and the extra yolks add, “a fattiness that counters the tart curd.”
When the mixture in the bowl is smooth, Isbell adds a blend of flour, baking powder, and salt, tapping in a little at a time and giving the beater a few turns around the bowl in between. When the last of the flour is in, she mixes just until the whole thing comes together into a soft, buttercup yellow dough.
Finally, Isbell adds the flavorings: seeds scraped from a vanilla bean, a hodgepodge of citrus zests, and enough poppy seeds to make you flunk a drug test. When these have been thoroughly blended in, she scoops the dough from the bowl, divides it into several pieces, and wraps each in plastic. It’s too sticky and malleable to roll out immediately, so she’ll put it in the fridge to firm up for at least an hour.
In the meantime, Isbell starts the curd. The exact blend of citrus changes from batch to batch, but this time she’s using a combination of orange, lemon, and a little grapefruit. In a wide bowl set over a pot of water simmering gently on the induction burner, Isbell mixes eggs, sugar, and both juice and zest from the citrus blend of the day. After giving the whole thing a good whisk, she’ll leave it alone for a while to cook over the gentle, steady heat of the double boiler.
It’s a slow process to make curd this way: It takes about 20 minutes for the curd to reach 82º C, which is when, Isbell sees that the egg is perfectly cooked. During that time, Isbell only needs to stir once or twice to make sure the edges aren’t overheating. There are faster ways to make curd — in a pot directly over the burner, for example — but Isbell says that low heat is better for the eggs. Egg proteins tighten and clump in higher heat (think scrambled eggs), so cooking low and slow keeps curd silkier and lump-free.
When the curd finally reaches temperature, Isbell adds butter for creaminess, gelatin for body, and citric acid for extra sour punch (since this curd is made with sweeter citrus fruits as well as lemon, it needs it). Then she immersion-blends the whole thing until it’s smooth and puts it in the fridge to cool and thicken.
Meanwhile, the dough is ready to roll out. Isbell positions a poppy-flecked disk between two pieces of parchment paper and begins gently rolling it out into a wide circle. A ring traced in Sharpie on the underside of the parchment provides a guideline for size. As it’s rolled, the dough warms up and softens again, so when she’s finished flattening both top and bottom crust, Isbell slides both disks into the freezer to firm up again.
Half an hour later or so, when the dough is sturdy but still supple and not completely frozen, Isbell assembles the cake. She lowers one disk into a greased, parchment-lined, cake pan, gently pressing it down and into the corners. She pinches and molds the sides of the crust so that they’re thicker near the top and sturdy enough to hold the top crust.
With the edges roughly shaped, Isbell grabs a pastry bag full of curd from the fridge and pipes a spiral of thick curd over the base of the cake. The bag is for speed and consistency: Isbell portions out the exact amount of curd needed for one cake into pastry bags in advance, so it’s easy to make every cake the same without stopping to measure out its contents.
After carefully setting the top crust down over the curd, Isbell presses down around the sides to make sure top and bottom are sealed tight. Then she slices the extra dough away from the edges, setting it aside for another cake. “Most doughs you can re-roll once,” she says. More than that, and they’ll be tough and chewy. But since the trimmings from three cakes usually yield enough to make a fourth, once is worthwhile.
The cake usually goes into the freezer again before being baked, since the slower bake gives it a better consistency. It comes out of the oven brown and crisp around the edges, and once it’s had some time to cool, Isbell flips it on onto a rack set over a sheet pan. The bottom now becomes the top, since its smooth surface and sharp edges look cleaner, and will better show off the sheen of the glaze Isbell now pours generously over the cake.
It’s a simple glaze, just a mixture of powdered sugar and grapefruit juice, which Isbell likes because it adds a faint blush to the icing. The light rosy hue, she says, matches the restaurant’s pink ceramic cake stand.
When Isbell cuts a fresh slice of the gateau au citron, the fresh glaze runs and drapes over its sides, pooling on the plate. It is all the adornment this bright, humble little cake needs.