recipe

“I thought it was the best cake I’ve ever had in my life. The mayo made it so moist it melted in my mouth!” —­Henry, recipe tester, age 9

safety
  • Uses the oven
  • Uses the microwave
  • Uses a knife
difficulty
  • Beginner
time
  • 1 hour and 10 minutes, plus 2 hours cooling time
yield
  • Serves 12

hey curious cook—

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Prepare Ingredients

Vegetable oil spray
1½ cups (7½ ounces)
all-­purpose flour
1 cup (7 ounces)
sugar
½ teaspoon
baking soda
¼ teaspoon
salt
½ cup (1½ ounces)
Dutch-­processed cocoa powder
⅓ cup (2 ounces)
chocolate chips
1 cup (8 ounces)
water
⅔ cup
mayonnaise
1
large egg
2 teaspoons
vanilla extract
Confectioners’ (powdered) sugar (optional)

Gather Baking Equipment

8-­inch square metal baking pan
2
bowls (1 large, 1 medium)
Whisk
Liquid measuring cup
Oven mitts
Rubber spatula
Toothpick
Cooling rack
Small fine-­mesh strainer for dusting with sugar
Cutting board
Chef's knife
1
 
Vegetable oil spray

Adjust oven rack to middle position and heat oven to 350 degrees. Spray inside bottom and sides of 8-­inch square metal baking pan with vegetable oil spray. Line bottom of baking pan with 8-­inch square piece of parchment paper.

 
2
 
1½ cups (7½ ounces)
all-­purpose flour
1 cup (7 ounces)
sugar
½ teaspoon
baking soda
¼ teaspoon
salt
½ cup (1½ ounces)
Dutch-­processed cocoa powder
⅓ cup (2 ounces)
chocolate chips

In medium bowl, whisk together flour, sugar, baking soda, and salt. In large bowl, combine cocoa and chocolate chips.

 
3
 
1 cup (8 ounces)
water

Heat water in liquid measuring cup in microwave until hot and steaming, 1 to 2 minutes. Use oven mitts to remove measuring cup from microwave. Carefully pour water over chocolate mixture and whisk until smooth. Let mixture cool for 10 minutes.

 
4
 
⅔ cup
mayonnaise
1
large egg
2 teaspoons
vanilla extract

Add mayonnaise, egg, and vanilla to cooled chocolate mixture and whisk until combined. Add flour mixture and use rubber spatula to stir until just combined and no dry flour remains.

 
5
 

Use rubber spatula to scrape batter into parchment-­lined baking pan and smooth top (make sure to spread batter into corners to create even layer).

 
6
 

Place baking pan in oven. Bake until toothpick inserted in center of cake comes out clean, 34 to 38 minutes.

 
7
 

Use oven mitts to remove baking pan from oven (ask an adult for help). Place baking pan on cooling rack and let cake cool completely in pan, about 2 hours.

 
8
 
Confectioners’ (powdered) sugar (optional)

Remove cake from baking pan and discard parchment (click here to learn how to remove a cake from its baking pan). Dust cake with confectioners’ sugar. Cut cake into pieces and serve.