Chocolate Mayonnaise Cake (Bizcocho de Chocolate con Mayonesa)

Chocolate Mayonnaise Cake has been a home-baking trick since the Depression and war-ration years, when eggs and oil ran short but a jar of mayonnaise sat in every icebox. The insight still holds: mayonnaise is just egg and oil, already whisked together, so swapping it in makes a chocolate cake that stays moist for days without a stand mixer or a single separated egg.

What You’re Learning

Mayonnaise is an emulsion, not a flavor. Mayonnaise is egg yolk and oil whisked together until stable, which is exactly what a cake recipe is already asking you to do by hand with a whisk and a bowl. Once it is baked into the batter alongside cocoa and sugar, no mayonnaise flavor survives. What is left is a crumb that stays tender and moist longer than a butter-creamed cake does, since the eggs and oil are already perfectly combined instead of fighting each other.

Hot liquid blooms the cocoa. Whisking hot coffee or hot water into cocoa powder dissolves it fully and wakes up its flavor, the same trick behind most good chocolate cakes. The batter will look thin, almost like pancake batter, right after mixing. That is correct, not a mistake, and it is exactly what keeps the baked cake from turning dense.

Ingredients

• 2 cups all-purpose flour
• 1 1/4 cups granulated sugar
• 1/2 cup unsweetened cocoa powder
• 1 1/2 tsp baking soda
• 1/2 tsp salt
• 1 cup mayonnaise
• 1 cup hot brewed coffee (or hot water)
• 1 tsp vanilla extract
• 1 cup heavy cream
• 8 oz semisweet chocolate, chopped
• Pinch of salt, for the ganache

Method

1. Heat the oven and prep the pans. Preheat to 350°F. Grease two 8-inch round cake pans, line the bottoms with parchment, and grease the parchment too.
2. Whisk the dry ingredients. In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt until no lumps of cocoa remain.
3. Add the mayonnaise and coffee. Add the mayonnaise, hot coffee, and vanilla to the dry ingredients. Whisk until completely smooth, about 1 minute. The batter will be thin, that is correct.
4. Divide and bake. Divide the batter evenly between the pans and bake 30 to 35 minutes, until a toothpick inserted in the center comes out clean.
5. Cool completely. Cool in the pans 10 minutes, then turn out onto a wire rack and cool completely, at least 1 hour, before frosting.
6. Make the ganache. Heat the heavy cream until it just starts to simmer. Pour over the chopped chocolate and a pinch of salt, let sit 2 minutes, then whisk until smooth and glossy.
7. Let the ganache thicken. Let the ganache sit at room temperature 15 to 20 minutes, stirring occasionally, until it thickens to a spreadable consistency.
8. Frost and stack. Spread a layer of ganache on top of one cake layer, top with the second layer, then cover the top and sides with the remaining ganache.

Notes

• Use plain mayonnaise, not “light” or flavored versions. Full-fat mayonnaise has the oil content this cake depends on for moisture.
• Hot coffee deepens the chocolate flavor without tasting like coffee. Hot water works too, just with a slightly less intense chocolate flavor.
• The batter will look thin. That is correct. A thin batter is what keeps this cake moist instead of dense.
• Let the layers cool completely before frosting, or the ganache will slide right off warm cake.
• No stand mixer needed. This is a whisk-and-bowl cake from the batter to the ganache.
• Store covered at room temperature up to 3 days, or refrigerate up to a week. Bring to room temperature before serving.