Sweet Potato Cake Recipe

Happy Halloween! When I thought of Halloween last year, disjointed memories come to me. It was around the week when our district's electricity got knocked out by a faulty electric grid late in the night, plunging the residential halls, as well as most of our campus, into a sudden darkness. Unable to study, and frankly, sick of studying by that time, we decided to explore the blacked-out campus by way of torchlight. The buildings, cloaked in darkness, lent our usual path the air of unfamiliarity, and the harsh flare of emergency lamps threw up startling shadows onto the shrubbery. It was dark and gusty, and rain from a previous shower kept the grass damp and the pavements shimmering. But the stars were brighter than I've seen before, bringing to the dark night a paradoxical serenity. What a night! - and perhaps, the scariest part of that story was that a year had passed us since then. 

Halloween seems to be a predominantly US tradition, and nobody elsewhere seems to think that it's a big deal. Small pockets of community, for example where R stays in Singapore, do seem make an annual event out of it, but it doesn't seem to be a national celebration in either Singapore or Australia. When Halloween decorations started appearing some houses around my neighbourhood, perhaps it's a sign that we should stock up on candy for hopeful trick-or-treaters? Last year, a group of us did a Halloween dinner where I brought a Pumpkin Cake, and this year, we're doing the a potluck again, this time with a Halloween theme dress-up. Maybe we can go treat-and-treating too after dinner?

Pic by rainer

Ever since my trip to Jinshan Old Street in Taiwan, I had developed a new-found appreciation for what one can do with root vegetables. The region of Jinshan heavily exports sweet potato and yam. Walking down the streets of Jinshan, root vegetables play a big role in many of their restaurant dishes, and many of their pastry stores feature them prominently even in desserts. We were plied with heaps of delicious pastries, from Western pull-apart breads to flaky Asian-style pastries - you name it, they have it, and with root vegetables to boot. There's an annual competition featuring Taiwan's most creative pastry, and the overall winner was naturally from Jinshan. 

Traditional Chinese desserts uses plenty of root vegetables, but it's one thing to make sweet soup-based desserts, and another in western-style cakes. There's plenty of carrot cake recipes, and pumpkin cakes alongside, but for the most part, my search for such recipes has yield surprisingly few results. 

While rifling through the Brown Betty's Cookbook, I paused at the Only for Eliza cake - one of their best-selling cakes, and finally, a cake based on sweet potato! Because life can't be easy, I neglected to take down the recipe, confident in my knowledge that I should be able to find a recipe floating online... which, of course, I couldn't find one. Drat! Luckily, I found a similar recipe from Amy, and gave it a go. 

Well, it took a couple of attempts. On my first go, I attempted to make a cake in the Brown Betty's Bakery style - a cake taller than it is wide, towering majestically with frosting between every layer. A stainless steel tin which I normally used to brew hot drinks was used to make the cake. Unfortunately, I should have baked the cake layers in several batches instead of one big go, because once I sawed through my giant tall cake into layers, the bottom and middle layers were too moist to withstand the weight and collapsed into a not-altogether-attractive pile. Also, I frosted the cake before it cooled thoroughly, and the buttercream melted into a greasy puddle. If I was aiming to build a towering cake, it looked like someone had applied a wrecking ball to the structure. Mea culpa. But to the credit of the recipe, the ruinous pile tasted good enough for the cake to be devoured in no time. The second attempt, I baked in a regular square pan. 

HOLIDAY SWEET POTATO CAKE

Recipe adapted from Amy from She Wears Many Hats
Makes one two-tiered 9-inch cake

Sweet potato puree is relatively easy to do: 2kg raw sweet potatoes makes about 750g. Bake whole raw sweet potatoes skin-on at 160C for about 45 minutes, until a fork goes in all the way through. Remove skin and process until smooth. Puree can be passed through a metal sieve for a smoother consistency, which I recommend. I also find that the taste of flour gets accentuated in cakes that have been kept in the fridge, which I dislike. I kept the quantity of flour as per the original recipe - 350g - but would look to adjust it to 300g the next time I bake. (Although I'd not tried the adjusted ratio, so would not recommend it yet. Watch this space!)

INGREDIENTS

350g (2 1/2 cups) all-purpose flour
2 teaspoons baking soda
2 teaspoons baking powder
1/2 teaspoon salt
1 tablespoon ground cinnamon
1 tablespoon ground ginger
226g (16 tablespoons/2 sticks) unsalted butter, room temperature
400g (2 cups) granulated sugar
3 large eggs, lightly beaten
1 tablespoon vanilla extract
550g (2 1/2 cups) mashed cooked sweet potatoes, cooled (about 4-5 sweet potatoes)
245g (1 cup) whole buttermilk (substitute 1 tbsp of lemon/vinegar + milk, and let stand for 5 minutes)

STEPS
1. Preheat oven to 175C (350F). Butter and flour two 9-inch cake pans, and line the bottoms with baking paper. If adding lemon/vinegar to milk, do so now. 

2. In a medium bowl, whisk flour, baking soda, baking powder, salt, cinnamon, and ginger together. Set aside.

3. In a large bowl, beat butter and sugar on medium-high for 4-5 minutes until the mixture lightens and becomes creamy. Add beaten eggs, one at a time, beating between each addition. Continue to beat on medium-high for 1-2 minutes until combined and fluffy. Add vanilla and sweet potatoes and mix until smooth. 

4. Add 1/3 of the flour mixture into the butter mixture, then 1/3 of the buttermilk. Alternate between the flour and milk into the butter mixture, stirring well after each addition. Beat on low speed until just incorporated.

5. Divide batter evenly between the cake pans. Bake at 175C for 35-45 minutes, until a toothpick inserted in the center comes out clean with no batter attached. Let cool in pan completely before frosting. 

NOTE
Online sources for a cup of mashed cooked sweet potato ranges from 200g to 328g, which has a wider range than I like. Given that yogurt and heavy cream is about 1 cup to 235g, I guesstimated 1 cup of sweet potato puree to be about 220g.