Satsumaimo Layer Cake

I don’t recall hearing the sing-song jangle of ice cream trucks during my time living in Japan, but I do remember a yakiimo cart that made its rounds near Yoshikawa station.  Yakiimo are warm,  whole roasted satsumaimo, Japan’s sweet potato with red skin and a white interior.  The cart owner would always be bellowing a steady song dedicated to the celebrated yakiimo.

To me, roasted satsumaimo are mouthwateringly good without any alteration; butter and sugar aren’t necessary.  When you do add those two ingredients into the equation, you’ll float away on a rich flavor cloud!

One popular treat in Japan are satsumaimo cakes, reformed into a small potato shape after mixing mashed satsumaimo with sugar, evaporated milk, butter, and a few other key ingredients.  There are even some regional Kitkats that are flavored after Japan’s ubiquitous sweet potato varieties.

This luxuriant layer cake is dedicated to the lovely, sweet tuber that has grown close to my heart.  Three layers of satsumaimo cake are topped with daigaku imo, a caramelized, candied version of the wonderful root.  The cake is slathered with kuromitsu (black sugar) cream cheese icing, and drizzled with kuromitsu syrup.

Taking a bite out of this cake reminds me of helping one of my host grandmothers tend to her satsumaimo crop in the garden.  There are so many moments in Japan that I hope to always carry with me, and rooting around in the dirt with someone I couldn’t communicate with well over the common goal of nurturing latent sweetness is definitely one that takes the cake.

Scroll down for the recipe!

Satsumaimo Layer Cake

For the Cake

Ingredients:

  • 2 1/2 cups all-purpose flour
  • 2 teaspoons baking soda
  • 2 teaspoons baking powder
  • 1/2 teaspoon salt
  • 1 tablespoon ground cinnamon
  • 16 tablespoons unsalted butter, room temperature
  • 2 cups granulated sugar
  • 3 large eggs, lightly beaten
  • 1 tablespoon vanilla extract
  • 2 1/2 cups mashed cooked satsumaimo sweet potatoes, cooled (about 4-5 sweet potatoes)
  • 1 cup buttermilk

Instructions:

  1. Preheat oven to 350 degrees. Spray two 6-inch round cake pans with canola oil. Line bottoms with baking parchment and spray the top of those too.
  2. In a large bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon.
  3. In the bowl of a mixer, beat together butter and sugar on medium-high for 5 minutes until creamy.  Don’t forget to scrape down the sides of the bowl, so all is well incorporated.  Add in eggs one at a time.  Beat on medium-high for 1-2 minutes until light and fluffy, scraping down bowl as needed. Add vanilla and sweet potatoes and beat until smooth, scraping down bowl as needed (scraping down the bowl is important stuff, y’all).
  4. Add the dry ingredients into the butter mixture, alternating with buttermilk. Beat on low speed until just incorporated.
  5. Divide batter evenly between pans. Bake at 350-degrees F for 45 minutes, or until toothpick inserted in center comes out clean.  Allow to cool for 15 minutes before removing the cake and placing on a cooling rack.  Torte each cake in half when the cakes are completely cool.

For the Frosting

Ingredients:

  • 2 tablespoons kuromitsu syrup 
  • 1 pinch cinnamon
  • 1 pinch salt
  • 4 cups powdered sugar, sifted
  • 1/2 cup butter, softened
  • 8 oz cream cheese

Instructions:

  1. Beat butter with the cream cheese on high, until light and fluffy.
  2. Gradually incorporate the powdered sugar
  3. Add the kuromitsu, salt, an cinnamon.  Beat until well incorporated

For the Daigaku Imo

Ingredients:

  • 2 satsumaimo, chopped into bite-sized pieces
  • 1/2 tablespoon black sesame seeds
  • 3 tablespoons vegetable oil (or another neutral-flavored oil)
  • 5 tablespoons sugar
  • 1/4 teaspoon soy sauce
  • 1/4 teaspoon rice vinegar

Directions:

  1. Wash the skin of the potato carefully.  You will not peel it.
  2. Cut the potato diagonally in the rangiri style – by rotating the potato a quarter between cuts.  Soak the pieces in water for 15 minutes to remove starch.  Change the water half way through.
  3. Wrap the lid of your frying pan with a kitchen towel and tie on the top near the handle.  By doing this, you prevent condensation from the lid dripping down onto the potatoes.
  4. Before turning your burner on, combine soy sauce, rice vinegar, sugar, and oil in your frying pan.  Stir well.
  5. Dry the potatoes with a towel before placing in your pan.
  6. Cover with your prepared lid and turn the stove on to medium heat.  Every two minutes, open the lid and flip the potatoes so that all sides are cooked.
  7. Cook in this style for approximately 10 minutes.
  8. Take off the heat and sprinkle with black sesame seeds, to taste.

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