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Sourdough Chocolate Cake with Ermine Frosting

Ingredients

Scale

For the Sourdough Chocolate Cake-

1 cup (2 sticks) unsalted butter

1/3 cup (33 grams)  Dutch-processed cocoa powder

1 teaspoon Kosher Salt

1 cup whole milk

1 3/4 cups (350 grams) granulated sugar

2 cups (240 grams) all-purpose flour, sifted

1 1/2 teaspoons baking soda

2 large eggs, at room temperature

1/2 cup stirred-down sourdough starter (ripe or discard)

1 teaspoon pure vanilla extract

For the Ermine Frosting-

1/3 cup + 1 tablespoon (50 grams) all-purpose flour

1 cup (200 grams) granulated sugar

1 cup whole milk

1 cup (2 sticks) unsalted butter, at room temperature

1 teaspoon pure vanilla extract

pinch of Kosher salt

Instructions

For the Sourdough Chocolate Cake-

Preheat oven to 350°F. Butter a 9×13″ metal baking pan.

In a medium saucepan set over medium heat, combine butter, cocoa, salt, milk, and sugar until melted. Remove from heat and let cool slightly.

In a large bowl, whisk together flour and baking soda. Add cocoa mixture and whisk until combined. Add eggs, sourdough starter, and vanilla, whisking until smooth.

Pour cake batter into prepared pan and smooth surface of batter with spatula.

Bake at 350°F for 30-35 minutes until toothpick comes out clean.

Let cool then cover tightly with plastic wrap. This cake is best the day after it is baked.

For the Ermine Frosting (aka Boiled Milk Frosting or Roux Frosting)-

In a medium saucepan set over medium-low heat, combine the flour and sugar, whisking constantly for about 2 minutes to cook the flour.

Slowly drizzle in the milk, whisking constantly until combined thoroughly. Raise heat to medium-high and continue whisking constantly until thickened. This will take several minutes. Once mixture begins to boil, continue whisking until it reaches the consistency of pudding or a thick caramel sauce.

Transfer mixture to a bowl and cover the surface with plastic wrap to prevent a skin from forming. Refrigerate 30 minutes or until completely cooled.

In the bowl of a stand mixer fitted with the whisk attachment, beat the butter until light and fluffy, about 3 minutes. With the mixer running at medium speed, gradually add the cooled milk mixture by the spoonful, allowing to combine between each addition, scraping down the bowl as needed. Add salt and vanilla. Raise the speed to high and beat until very light and fluffy.

Switch to the paddle attachment and beat a few more minutes. This helps smooth out some of the air bubbles and helps the frosting to spread into a smooth surface.

Use immediately. Any leftover icing should be refrigerated. Let come to room temperature before serving.

Notes

Be sure to use sourdough starter that is ripe (i.e. had time to double in size after being fed). Discard is fine too. Do not feed the starter immediately before using in this recipe. Sour cream can be substituted for the sourdough starter in this recipe.

Ermine Frosting is an old-fashioned recipe that is also sometimes referred to as Boiled Milk Frosting or Roux Frosting. It is the traditional frosting for Red Velvet Cake.