Six years ago, I developed a recipe that—much to my surprise—turned into a sensation. It was for an uncomplicated, unassuming cake, albeit one with a twist: Instead of butter, the batter was enriched with extra-virgin olive oil, the fruitiness of which was subtly boosted with a tiny dose of grated lemon zest. Rather than frosting, this exquisitely simple offering sported a charming crackly sugar crust. Readers were delighted by the way the cake came together quickly using everyday ingredients; how its fine, plush crumb contrasted with its crinkled top; and by the notion that it could be enjoyed plain with an afternoon cup of tea or gussied up with garnishes for a dinner party.
The use of olive oil was intriguing, and many cooks enjoyed surprising guests by revealing the “secret ingredient.” But the oil has another advantage: An oil-based cake tastes softer and moister than a butter cake, because oil is fluid at room temperature whereas butter is solid.
Aficionados baked the cake so frequently that they started to tweak it, substituting orange or lime zest for lemon; using infused olive oil; and adding flavorings such as cardamom, anise seeds, or rosemary. Occasionally, a reader would inquire about a chocolate version—chocolate and olive oil are so lovely together—and I’d reply that such a change would require an extensive reformulation. Well, here it is.
Here’s how my original cake came together: I whipped eggs, sugar, and lemon zest in a stand mixer until the mixture was voluminous and pale yellow and then drizzled in extra-virgin olive oil. I mixed in half of the dry ingredients—all-purpose flour, baking powder, and salt—followed by milk, followed by the remaining dry ingredients. I scraped it all into a greased springform pan, sprinkled sugar on top, and baked it.
Now to make it chocolate. It may seem like the easiest way to turn a nonchocolate cake chocolate is to swap a portion of the flour for an equal portion of cocoa powder. After all, cocoa powder has the same dry, starchy qualities of flour as well as a higher proportion of flavorful cocoa solids than any other form of chocolate, so it tastes more intensely chocolaty. But the reality is more complex: Cocoa powder isn’t just unsweetened; unlike the flour it’s replacing, it’s downright bitter. If you don’t add more sugar, the cake will taste unbalanced. But extra sugar can weigh down the batter, possibly causing the cake to fall. Would that happen here?
Science: These Two Starches Aren’t Interchangeable
If you’re sweet on chocolate, you may have considered converting a white or yellow cake into a deep, dark, fudgy one by replacing a portion of the flour with cocoa powder, a starchy source of pure, assertive chocolate flavor. Not so fast: The starch in cocoa powder is unusually high in amylose, and in general, the higher the amylose, the more viscous a gel a starch makes. Thus, a batter that contains cocoa powder bakes up stiffer than an all-flour one does, so it eats drier. You’ll need to add extra liquid to the batter lest the cocoa starch dry out your creation.
Flour and cocoa powder contain different types of starch, so they can’t be swapped one-for-one. To demonstrate this, we mixed each ingredient with the same amount of water: Flour turned moist, whereas cocoa powder was stiff and pasty.
There was only one way to find out. I decreased the flour to accommodate 2 ounces of cocoa powder and increased the sugar by about 20 percent. This cake didn’t collapse, but even with all of the olive oil, it was on the dry side and a bit dense.
It turns out that cocoa powder forms a stiffer mixture with water than flour does, and that was contributing to the dryness. For my next attempt, I not only halved the cocoa, but I also decreased the flour even more. With less cocoa, I’d need to supply more chocolate flavor, so I opted for 3 ounces of the bittersweet kind, which I melted into the olive oil.
This cake was superchocolaty, remarkably moist, and—with the flour (and, consequently, the amount of gluten) so reduced—very tender. However, there were still modifications to be made.
The fine crumb and slightly bouncy texture of the original cake came from the tiny air bubbles created by whipping the eggs and sugar in a stand mixer. But the olive oil–and-chocolate mixture was heavier than the olive oil alone had been, so the batter for this cake deflated as soon as I added it. Since the mixer wouldn’t aerate this batter in the same way as the original, I decided to see what would happen if I mixed it by hand. After combining the sugar and eggs, I whisked in the olive oil–and-chocolate mixture and the milk. I finished with the dry ingredients, to which I added baking soda in hopes that it would react with the liquids to inflate the batter. The process was so fast and easy that the batter was ready before the oven was fully heated.
Happily, this cake rose beautifully even without the use of a mixer. It was now nearly perfect, aside from an aesthetic issue: The sugar that I’d sprinkled over the batter kept migrating to the center. There were two reasons. First, the loose batter heated up quickly at the edges; as it firmed and expanded, it pushed the more fluid batter toward the middle, shifting the crust. Second, the batter had difficulty finding purchase on the slick sides of the greased pan, so it folded in on itself rather rising straight up.
To tighten the batter just a bit, I removed a single egg white. I also wiped excess grease from the sides of the pan to make sure that the batter could climb as it baked. Now the sugar crust stayed put.
I placed the cake on a rack to cool, but instead of loosening the collar of the pan as I had for the original cake, I made a small upgrade by leaving it attached. As the cake sat, the collar trapped moisture that would have otherwise escaped, leaving the edges soft—a nice contrast to the crisp, sugary top.
Thank you, chocophile readers, for encouraging the creation of this new—dare I say sensational—cake.
Technique: Checking Olive Oil Cake for Doneness
The toothpick test—insert the pick into the center of a cake; if it emerges with a few moist crumbs attached, the cake is done—isn’t advised for olive oil cake. The pick will mar the sugar crust, and the crust can scrape off raw batter that clings to the pick, deceiving you into thinking the cake is done. Instead, insert a skewer diagonally into a crack, aiming for the center (a toothpick is too short to go deep enough).