Chocolate Mayonnaise Cake
An old-fashioned chocolate sheet cake made with mayonnaise instead of butter and eggs. Don't let the mayo scare you off. It's just oil and eggs already mixed together, and it makes one of the most tender, moist chocolate cakes you'll ever pull out of a 9x13.
Servings: 15 slices
Calories: 514kcal
Equipment
- 1 9x13-inch baking pan
- mixing bowls
- Whisk
- electric mixer
- rubber spatula
- Measuring cups and spoons
Ingredients
Cake
- ½ cup unsweetened cocoa powder
- 1 ¼ cups boiling water
- 2 cups all-purpose flour
- ¾ teaspoon baking soda
- 1 teaspoon baking powder
- ¾ teaspoon fine salt
- 1 cup full-fat mayonnaise
- 1 cup granulated sugar
- ½ cup light brown sugar packed
- 2 teaspoons vanilla extract
- 1 tablespoon unsweetened cocoa powder for dusting the pan
Chocolate Frosting
- ½ cup unsalted butter softened
- ⅓ cup unsweetened cocoa powder
- 3 cups powdered sugar
- ½ cup heavy cream plus 1-2 tablespoons more if needed
- 1 teaspoon vanilla extract
- 1 pinch salt
Instructions
Cake
- Heat the oven to 350°F, or 325°F if you're using a dark or nonstick pan. Grease a 9x13-inch pan and dust it with cocoa powder instead of flour so you don't end up with white streaks on a chocolate cake.
- Whisk the cocoa powder into the boiling water until completely smooth, then whisk in the granulated sugar and brown sugar while the liquid is still hot so they dissolve all the way. Let it sit for 10 minutes to cool to warm. This wakes up the cocoa so the cake tastes richer, and it brings the temperature down enough that the liquid won't break down the mayonnaise.
- In a separate bowl, whisk together the flour, baking soda, baking powder, and salt until there are no clumps.
- Whisk the mayonnaise and vanilla into the cooled cocoa mixture until smooth.
- Add the dry ingredients to the wet in two or three additions, whisking until the batter is completely smooth with no streaks or pockets of dry flour. The batter will be thin and pourable, and that's exactly right.
- Pour the batter into the prepared pan and get it into the oven right away.
- Bake 28 to 33 minutes, checking at 28. When the edges just begin to pull away from the sides of the pan, start testing the center. The cake is done when the center springs back to a light touch and a toothpick comes out with a few moist crumbs clinging to it. If the toothpick comes out completely clean, it baked a little too long.
- Set the pan on a wire rack and cool the cake completely before frosting.
Chocolate Frosting
- Beat the butter until creamy, then beat in the cocoa powder until fully incorporated.
- Add the powdered sugar gradually, alternating with the heavy cream. Beat in the vanilla and salt.
- Beat on medium-high for 2 to 3 minutes until smooth, glossy, and spreadable. Add another tablespoon of cream if it's stiff.
- Spread evenly over the cooled cake.
Notes
Pan and oven temperature: Dark and nonstick pans absorb more heat, so bake at 325°F if that's what you have. Light metal and glass pans go at 350°F. Either way the bake time stays about the same. Start checking at 28 minutes.
How to tell when it's done: Go by the cake, not the clock. The first sign is the edges just starting to pull away from the sides of the pan, which means it's time to start testing the center. The center should spring back when you press it lightly, and a toothpick should come out with a few moist crumbs. A completely clean toothpick means you've overbaked it. If you use a thermometer, the center should read 200 to 205°F.
Which mayonnaise: Use full-fat regular mayonnaise like Hellmann's, Best Foods, or Duke's. Skip Miracle Whip, which has added sugar and spices, and skip light or reduced-fat mayo, which cuts the fat roughly in half and will give you a dry cake.
Don't leave dry flour pockets: This batter is thin, so any unmixed flour won't work itself out in the oven. Whisk until it's genuinely smooth. There's enough fat in this batter that mixing it smooth won't make the cake tough.
Storage: Cover the frosted cake tightly and keep it at room temperature for up to 3 days, or in the refrigerator for up to 5 days. Let refrigerated slices sit out for 20 to 30 minutes before serving. To freeze, wrap the unfrosted cake or individual slices tightly and freeze up to 3 months, then thaw overnight in the refrigerator.
Nutrition
Serving: 1slice | Calories: 514kcal | Carbohydrates: 74g | Protein: 3g | Fat: 24g | Saturated Fat: 9g | Polyunsaturated Fat: 9g | Monounsaturated Fat: 6g | Trans Fat: 0.3g | Cholesterol: 34mg | Sodium: 424mg | Potassium: 111mg | Fiber: 2g | Sugar: 55g | Vitamin A: 322IU | Vitamin C: 0.03mg | Calcium: 27mg | Iron: 2mg
