For Extra Moist, Tender Cookies, Bring Some Potato to the Party

We’ve got the science and the recipes to show why this beloved tuber is the inconspicuous hero of baking.
For Extra Moist Tender Cookies Bring Some Potato to the Party
Ellis Parrinder

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The world may disagree on which side of the road to drive on, which unit of measurement to use, which football is the real football—the list goes on. But one thing we can all agree on is our collective love for the potato. Fried, boiled, mashed, or grilled—these tubers have a remarkable ability to withstand countless transformations, never forsaking taste or texture. They’ve also been around forever; as a food source of the Inca Empire since 8000 B.C. and as a fuel for the spread of European imperialism. "By feeding rapidly growing populations," writes historian William H. McNeil, potatoes "permitted a handful of European nations to assert dominion over most of the world between 1750 and 1950.”

While the prowess of potato is well documented in colonialism and cooking, only a few have harnessed its transformative qualities in baking. Potatoes—whether in mashed, flour, or starch form—have been a longstanding staple in German baking and a curious addition to cakes and breads in the US since the early 20th century thanks to their ability to retain moisture, which makes baked goods extra tender. In their new cookbooks, Bake Me a Cat and Baking Yesteryear, authors Kim-Joy and B. Dylan Hollis tap into this tuber’s baking potential to create two uniquely fun recipes that showcase the potato’s true potential.

Kim-Joy’s Bake Me a Cat is a cookbook bound with serotonin, with each page donning an adorable feline-shaped bake. Among these a-meow-zing (sorry!) recipes, the 3D cat cookies stood out to me the most. Cuteness had a lot to do with it, but what hooked me was how everything from the ears to the tails and the paws held its distinct shape once out of the oven—no spreading across the surface of the baking sheet or puffing up beyond recognition.

“These are German-style cookies, which have a unique melt-in-your texture due to a secret ingredient…potato starch!” writes the Great British Baking Show alum. Fascinated, I reached out to Kim-Joy to learn a bit more about the mechanics of this ingredient and learned that the melty texture is just the start. 

Potato Starch

“Potato starch doesn’t contain gluten and this means the overall gluten content in the dough is massively reduced, which is very advantageous, especially when creating anything that will need to be worked/manipulated more,” she explained over email. This means you can take your time perfecting every little detail of your cat cookie, and it won’t become overworked or tough in the oven.

In many baking recipes, cornstarch is often used to minimize spreading in cookies and to add a fluffy texture to bread, but anything cornstarch can do, potato starch can do better. “I ran out of potato starch one day and thought I’d just use cornstarch instead,” explains Kim-Joy, “but I found that these were drier and much less crumbly.” This led her to hypothesize that potato starch is better at retaining moisture—and she was right. A 2014 study by the Laboratory of Food Chemistry, Wageningen University and Research Centre in The Netherlands found that “pressed potato fibers (PPF), a by-product of starch production, has a high water-holding capacity.”

Potato flour, though often placed right next to its starch counterpart at grocery stores, doesn’t work as a direct substitute in this recipe for two reasons. First, potato flour is essentially whole potatoes, dried and milled, which makes it much coarser. The starch, on the other hand, is the dehydrated protein particles with fine, powdery consistency, extracted from compressed potatoes. And using flour instead of starch would compromise the smooth, melty texture of these cookies. The second reason is that potato starch is colorless and flavorless whereas potato flour still contains the tuber’s distinct flavor and light yellow hue. So unless you want your cat cookies to taste like potato, it’s best to stick to the starch.

In his cookbook Baking Yesteryear, B. Dylan Hollis incorporates half a cup of cooled mashed potato into the batter of his double chocolate potato drop cookies—a cue he took from a chocolate potato cake that dates back to 1912. In those days, mashed potatoes were used in baked goods “to give them some added cakey/chewiness/softness that could not be achieved as easily otherwise,” he explained to me over email. The Fort Walla Walla Museum in Washington mentions on its website that “potato was a popular addition to cakes during World War I, the Great Depression, and World War II due to shortages of butter and flour.”

In Hollis’s recipe, the potato’s moisture-retaining powers are in full effect. The cookies are pillowy and cakey, reminiscent of an exceptionally soft black-and-white cookie. The delicate potato flavor pairs surprisingly well with the bitter chocolate. But the most functionally fascinating part is that these cookies remain super tender when left uncovered at room temperature for days. A 2020 study in the Food Science and Nutrition Journal explains this phenomenon—it states that the presence of potato in baked goods (bread, in this case) prevents the wheat starches from crystallizing, keeping it softer for a longer period of time.

If you’re wondering about substituting potato flour instead of mashed potato in baking, you’ll need to keep a few ratios to keep in mind. King Arthur Baking recommends using ¼ cup of potato flour for ¾ cup of mashed potatoes and increasing the total liquid amount by about 50% to make up for the lack of moisture in potato flour. I used this formula to make Hollis’s recipe: I used 35 grams of potato flour in place of 105 grams of mashed potato and increased the amount of buttermilk to 1¾ cups (keeping in mind the extra liquid in the butter and the egg). The end result was a cookie very similar to Hollis’s original recipe, maybe a touch drier due to the inconsistencies in the total amount of liquid.

Because of its ubiquity, the potato may seem like a simple, uncomplicated ingredient. But if these two recipes and a multitude of 20th-century books say anything, it’s that this beloved tuber is the inconspicuous hero of our kitchens. Who knows what other secrets it holds?