Chocolate Zucchini Cake with Swiss Buttercream
For the past year, chocolate cake has been my nemesis.
Cupcakes, bundt cakes, layer cakes, loaf cakes, you name it... everything failed. It was the same result every time: the batter was strangely light and airy, even when I carefully, slowly folded all ingredients until just mixed and repeatedly dropped the pan on the counter; once the batter was in the oven, I sat and waited and watched as it rapidly rose (and I mean rapidly) before overflowing and spilling all over the oven. It became customary for me to place a baking sheet underneath any chocolate cake I baked, and every time, it was a massive, fuming failure which ended in me angrily scraping burnt bits of chocolate cake off of the bottom of my oven.
The whole thing was a mystery to me, because it seemed I had tried everything. I decreased the amount of leavening in the recipes -- whether it be baking soda or baking powder -- and I tried recipes with less or thicker liquid, since it seemed the problem arose when I added the liquid ingredients to the dry ingredients. I was set on the fact that chocolate cake simply didn't work at a high altitude, but I knew that wasn't the case because I made a spectacular chocolate layer cake when I lived in Boulder.
I was stumped. And so I stopped trying.
And then I made the most amazing carrot cake of my life. It's not the altitude. It has to be something to do with the thickness of the batter (the carrot cake batter is very thick with carrots and nuts, so my brain that is not science-y at all came to the conclusion that the air in the batter had nowhere to go), and it has to be something to do with cocoa powder.
So I did some research, and I learned all about the difference between Dutch-processed cocoa powder and natural unsweetened cocoa powder. I had been using special dark cocoa powder, which is Dutch-processed, and which apparently is very, very different from natural unsweetened cocoa powder. We're onto something here.
From Joy the Baker:
"Dutch-processed cocoa powder is cocoa powder that has been washed in a potassium solution that neutralizes its acidity. The Dutching process also gives the cocoa powder a darker color. Dutch-processed cocoa powder in baking is usually paired with baking powder because, as mentioned in The Difference Between Baking Soda and Baking Powder, the baking powder takes care of the acid component in leavening our baked goods.
Was that too many words? Here’s a breakdown: Dutch-processed cocoa powder, acids stripped, dark color, reach for the baking powder!
Natural cocoa powder is cocoa that has not had its acid stripped. Natural cocoa powder is usually lighter in color, and because it has all of its acids in tact, it is usually paired with baking soda because the metallic taste that is released in the sodium carbonate of baking soda is mellowed by the acid in natural cocoa powder. Natural cocoa powder is what is typically found in American grocery stores. We’re talking Hershey’s Cocoa Powder… that’s natural cocoa.
Too many words again. Here’s a breakdown: natural cocoa powder, acids present, light in color, grab that baking soda!"
I know, it's confusing. But after reading it a few times, I decided I needed to try a chocolate cake recipe using natural cocoa powder. I also decided I needed to try a chocolate cake recipe that started with a thicker, heavier batter. And where did I land? Chocolate zucchini cake.
I knew I needed to find a recipe that was similar in make-up to the carrot cake. This one was spot on: shredded zucchini (like shredded carrots) and chocolate chips (like chopped nuts). The recipe relies heavily on baking soda (2 teaspoons!), so I planned to use natural unsweetened cocoa powder to balance out the acidity (and -- I hoped -- the leavening).
I made the batter.
I folded in the dry ingredients and the chocolate chips.
I whacked the pans on the counter before baking.
I sat in front of the oven for the full 32 minutes of bake time.
It was a roller coaster of emotions. There were times I was sure the cake was going to fail, and then by the time 20 minutes rolled around, I was elated. The cakes were perfect. And when they were layered and frosted and brought to a family dinner, they passed the 3 most important tests:
1. The Carson (chocolate cake fiend boyfriend)
2. The Jonathan (brother & former pastry chef)
3. The Nieces (picky, brutally honest 2 & 4-year olds)
FINALLY: I had succeeded with a chocolate cake recipe. I don't know whether it was the thicker batter or the cocoa powder that did it (or whether it was just pure luck), but this cake is off-the-charts delicious. I sliced the two 9-inch cakes in half to make a 4-layer cake, but be warned: if you choose to go this route, the cakes are very, very moist, which makes frosting and slicing a dangerous feat (chilling is necessary, and a crumb coat is very necessary). If you don't choose to go this route, leaving the 2 cakes as-is is perfectly fine, and they'll still be totally delicious. You can also make the cake in 8-inch pans, but the bake time will be longer by 10 or 15 minutes.
About the frosting: Swiss meringue buttercream will change your life. I'm not kidding. It's much more labor-intensive and time consuming than your traditional American buttercream, but the result is a silky smooth, mildly sweet frosting instead of a powdered sugar & butter bomb (which is American buttercream). BUT, if you're short on time or you prefer American buttercream (or if you don't have 8 egg whites and 3 cups of butter handy), then you do you.
Either way, find or make an excuse for this layer cake and invite some friends or family over -- just like anything sweet, it's so much better shared!
Chocolate Zucchini Cake with Swiss Buttercream
Adapted from Sally's Baking Addiction
For the cakes:
2 cups all-purpose flour
3/4 cup unsweetened natural cocoa powder
2 teaspoons baking soda
1/2 teaspoon baking powder
1 teaspoon espresso powder
1/2 teaspoon salt
1 cup vegetable oil
1 cup granulated sugar
3/4 cup light brown sugar
4 large eggs
1/3 cup sour cream or plain yogurt
2 teaspoons vanilla extract
2 1/2 cups shredded zucchini (about 2 large)
1 cup semisweet chocolate chips
For the Swiss buttercream:
8 egg whites, at room temperature
1 cup granulated sugar
2 1/2 cups unsalted butter (4.5 sticks), softened
1 cup powdered sugar, sifted
Pinch of salt
2 tablespoons vanilla extract or clear imitation vanilla, for a pure-white frosting
For the chocolate ganache topping (optional)
3 oz semisweet chocolate, chopped
1/4 cup heavy cream
2 tablespoons light corn syrup
Pinch of salt
Preheat oven to 350°F (177°C). Grease and flour two 9x2 inch cake pans, and line with parchment rounds. Grease the parchment. Set aside.
Make the cake: Whisk the flour, cocoa powder, baking soda, baking powder, espresso powder (if using), and salt together in a large bowl. In another large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the oil, granulated sugar, brown sugar, eggs, sour cream, vanilla, and zucchini together until combined. Pour into dry ingredients and fold batter until completely combined. Fold in the chocolate chips. Batter will be slightly thick. If you see air bubbles in the batter, pick up the pans and drop them onto the counter a few times.
Pour batter evenly into cake pans. Bake for around 32 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, it is done. Allow cakes to cool completely in the pans set on a wire rack. When the cakes are cool, carefully flip cakes onto the wire rack and wrap each cake tightly in plastic wrap. Chill in the refrigerator until you're ready to frost -- I chilled mine overnight.
Slice the cakes: If you're making a 4-layer cake, use a serrated knife to slice each cake in half. If this makes you nervous, this is an excellent tutorial on how to properly level and slice your cakes. If this makes you really nervous, don't slice the cakes and make a 2-layer cake. It's still going to be fabulous. Allow sliced layers to chill in the fridge while you make your frosting.
Make the frosting: Over a double boiler, heat the whites, granulated sugar and salt, whisking constantly, until the sugar dissolves and the mixture feels warm.
Place the mixture in a stand mixer and whip on high until a peak forms and the mixture is cool, about 5 minutes.
Turn the mixer to medium speed and add the softened butter a little at a time, beating after each addition. Depending on your climate, you may need more or less butter - go with your gut. Add the powdered sugar and vanilla and mix until combined.
Crumb coat: Place 1 cake layer on your cake stand or serving plate. Evenly cover the top with frosting. Top with 2nd layer and repeat. Repeat with remaining layers, and frost the top and sides of the cake with a light layer of buttercream. If you have a bench scraper, use it to evenly spread the icing along the cake. Don't worry about crumbs getting into your frosting - this is our crumb coat. Place the cake in the fridge for 20-30 minutes.
Make the ganache, if using: Place chocolate in a heat-safe bowl and set aside. In a small saucepan, gently bring heavy cream to a slow simmer. Pour over chocolate and let sit for 2 minutes without mixing. After 2 minutes, whisk chocolate and cream until smooth. Place in the fridge for 15 minutes.
Frost that cake: Retrieve the cake from the fridge and finish with the remaining frosting, using your bench scraper to even the sides and the top. Get fancy and throw some sprinkles on there, if you want -- or keep it simple. Once ganache has cooled, spoon and spread over the top of the cake, allowing the ganache to come to the edges. If you're a fan of those drippy cakes, let it drip down the sides.
Cover any leftover cake and store at room temperature for 2-3 days or in the refrigerator for up to 5 days.