Long-Fermented Sourdough Chocolate Cake (moist and fluffy!)

My first love of baking began as a cake baker and decorator, and nothing feels quite as indulgent as a tender slice of chocolate cake with a cloud of fluffy buttercream. Once I discovered sourdough, I became fascinated with bringing the same fermentation magic into my cakes. After plenty of testing (and a few tears), I finally perfected this Long-Fermented Sourdough Chocolate Cake- a recipe that's moist, fluffy, and rich, with all the added benefits of sourdough starter and fermentation.

5 from 1 vote

Print Recipe

Prep Time 1 1

Cook Time 45

Servings 12

Equipment

3 Mixing bowls
Whisk
Kitchen scale (optional)
Measuring cups and spoons
Cake pans (2 9 in round pans or 1 9x13 pan)
Parchment paper (optional- to line pans)
Hand beaters or stand mixer
Cooling rack
Toothpick or cake tester
Offset spatula (optional- for icing cake)
Sieve or sifter
Cake stand or platter
Pastry bags and tips (optional- for decorating cake)

Ingredients

Long-Fermented Sourdough Chocolate Cake

Wet Ingredients:

1/2 cup (120g) sourdough discard
2 cups (400g) granulated sugar
⅔ cup (160g) full-fat sour cream
1 cup (240g) whole milk or buttermilk
3/4 cup (165g) avocado oil (hold back 1/4 cup see notes below)
2 large eggs room temp
2 large egg yolks room temp
¼ cup (56g) unsalted butter melted & slightly cooled
2 teaspoons vanilla extract
¼ cup (80g) hot water or brewed coffee slightly cooled
¼ teaspoon instant espresso powder

Dry Ingredients:

2 ¾ cups (325g) all-purpose flour
¾ cup (64g) Dutch-process cocoa powder
1 ½ teaspoons baking powder
½ teaspoon baking soda
1 teaspoon fine sea salt

Fudgy Whipped Buttercream

Ingredients:

8 oz (226g) good-quality dark or semisweet chocolate chips
1 cup (226g) unsalted butter room temp
½ cup (50g) Dutch-process cocoa powder
½ teaspoon fine sea salt
¼ teaspoon espresso powder optional
3 ½ cups (420g) powdered sugar sifted
½ cup (120g) heavy cream cold
2 teaspoons vanilla extract

Instructions

Step 1: Mix Fermented Base

The night before you want to bake your cake, ferment the base of your batter. In a bowl, combine with a whisk the flour, cocoa powder, sourdough discard, white sugar, sour cream, buttermilk or milk, and 1/2 cup of avocado oil (reserve 1/4 cup for later).
1/2 cup (120g) sourdough discard, 2 cups (400g) granulated sugar, ⅔ cup (160g) full-fat sour cream, 1 cup (240g) whole milk or buttermilk, 3/4 cup (165g) avocado oil, 2 ¾ cups (325g) all-purpose flour, ¾ cup (64g) Dutch-process cocoa powder
Cover the bowl with plastic wrap, and refrigerate overnight. This step is key in your fermentation process. If you want to shorten your fermentation time, you can allow the batter to rest for 4 hours at room temperature for a same day bake. I don't advise leaving this batter at room temperature overnight, its too hydrated and will overproof.

Step 2: Finish Mixing Batter

The next day, remove bowl of batter from refrigerator and allow to rest on the counter for roughly 4 hours. This is a key step to achieving a tender crumb, don't skip this step! If you like temperature cues, the temperature of the batter should read roughly 70 F before proceeding.
If you allowed batter to rest on the counter and did not refrigerate or you're doing a quick bake, skip this step of resting.
In a medium mixing bowl, add your eggs and egg yolks. Add the remaining 1/4 cup of avocado oil and your melted butter (slightly cooled). Add vanilla. Whisk this mixture together until pale and smooth. Set aside.
2 large eggs, 2 large egg yolks, ¼ cup (56g) unsalted butter, 2 teaspoons vanilla extract
Next, brew the amount of coffee you need or mix your hot water and espresso powder together. Set this aside.
¼ cup (80g) hot water or brewed coffee, ¼ teaspoon instant espresso powder
To the bowl of your base batter, add the egg/oil/butter mixture. Whisk until smooth or use hand mixers ON LOW to incorporate the batter. To avoid a tight and tough cake, mix ingredients as gently as possible. This means mix until just incorporated and if using hand beaters, use the lowest setting.
Sprinkle baking powder, baking soda, and salt into the batter. Mix until just combined.
1 ½ teaspoons baking powder, ½ teaspoon baking soda, 1 teaspoon fine sea salt
Lastly, pour the hot coffee or espresso into the batter and mix until just combined.

Step 3: Bake Cakes

Preheat oven to 350°F (175°C). Grease and lightly flour two 9-inch pans or one 9x13 baking pan. I strongly recommend lining the very bottom of the pan with parchment paper at this time, this helps the cake release evenly.
If using 2 9-inch cake pans, divide batter evenly between the two pans. This should roughly be 2 1/4 cups batter per pan. If using a sheet pan, pour all of the batter into the pan.
Set your timer for 40 minutes. Check cake at 40 minutes, inserting a toothpick to check doneness. This cake takes me anywhere between 40-45 minutes to be done. When the cake is done, a toothpick should come out with a few moist crumbs but not with wet batter. When you touch the top of the center of the cake, it should be firm and not overly glossy.
Note: If chocolate cake is under done, when cake is removed from heat the center will fall. If you overbake the cake, it will err on the side of being dry. Go slow and check frequently after the 40 minute mark to ensure the cake is baked properly without losing moisture. Use the notes above to make sure cake is baked correctly.
When cakes are done cool slightly in pans, then turn out onto racks. Allow to cool completely. If desired, trim any uneven tops and wrap in plastic. Freeze cake while you prepare your frosting.

Step 4: Make Chocolate Frosting

In a microwave safe bowl, melt chocolate chips. Heat at 30 second intervals, stirring between. You want chocolate to be melted and smooth. I achieved this consistency with 3 30-second intervals in the microwave. Be careful overheating your chocolate or it will stiffen and be hard to work with. Allow to cool.
8 oz (226g) good-quality dark or semisweet chocolate chips
In a stand mixer or a large bowl, add your butter. Cream on high for 3-4 minutes until pale and fluffy.
1 cup (226g) unsalted butter
Sift in cocoa powder, and add salt and espresso powder to frosting if using. Whip on medium high until frosting is smooth.
½ cup (50g) Dutch-process cocoa powder, ½ teaspoon fine sea salt, ¼ teaspoon espresso powder
Add cooled melted chocolate to the frosting. Whip on high until frosting is glossy and smooth.
Add sifted powdered sugar to icing. Beat sugar into icing. At this point the icing may look very stiff. Don't worry!
3 ½ cups (420g) powdered sugar
Add vanilla and half of the cream to the icing. Whip on high until frosting starts to become light and fluffy. Add remaining cream in 1 Tablespoon intervals until the frosting has achieved your desired consistency. Chill for a few minutes in the refrigerator if icing is very soft. It won't need long, so keep an eye on it.
2 teaspoons vanilla extract, ½ cup (120g) heavy cream

Step 5: Frost Chocolate Cake

For a two-tier cake: If frosting a two-tier cake, remove cakes from the freezer, and place 1 cake upside down on cake stand. I like to put a dollop of icing on the cake stand first to help the cake stick to the stand. Use half of the chocolate icing to frost the 1st layer of cake.
When first layer of cake is smoothly covered in icing, place second layer upside down on top of the first. Use remaining frosting to cover the top and sides of the second layer, leaving some left over icing if you want to pipe any decorative details. I piped small swirls around the base of my cake and on the top, then garnished with shaved chocolate.
For a single sheet cake: turn cake upside down onto serving platter. Spread frosting over the top and sides of the entire cake, smoothing with a spatula. Decorate cake if desired with left over frosting and shaved chocolate.
Slice cake and serve!

Course Cakes and Pies

Cuisine Cakes