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Decadent Dark Chocolate Sheet Cake with Rich Cocoa Frosting

This elegant dark chocolate sheet cake is the ultimate crowd-pleaser with its intense cocoa flavor and less sweet profile, perfect for potlucks and special occasions. The moist, dark crumb and rich frosting come together in a simple oven-baked creation that stores beautifully and tastes even better the next day.
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Prep Time 15 minutes
Cook Time 35 minutes
Total Time 50 minutes
Servings: 12 servings
Calories: 420
Ingredients Method Notes

Ingredients
  

Ingredients
  • 2 cups all-purpose flour
  • 1¾ cups granulated sugar
  • ¾ cup unsweetened cocoa powder (Dutch-process preferred)
  • 2 teaspoons baking soda
  • 1 teaspoon baking powder
  • 1 teaspoon salt
  • 2 large eggs, room temperature
  • 1 cup buttermilk
  • ½ cup vegetable oil
  • 2 teaspoons vanilla extract
  • 1 cup boiling water
  • ½ cup unsalted butter
  • ⅓ cup whole milk
  • ¼ cup unsweetened cocoa powder
  • 3 cups powdered sugar
  • 1 teaspoon vanilla extract
  • Pinch of salt

Method
 

Instructions
  1. Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan and set aside.
  2. In a large mixing bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt until well combined.
  3. Add eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients. Mix on medium speed until just combined, about 2 minutes.
  4. Carefully pour in the boiling water and mix on low speed until the batter is smooth. The batter will be thin – this is normal.
  5. Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
  6. Allow the cake to cool completely in the pan on a wire rack before frosting.
  7. For the frosting, melt butter in a saucepan over medium heat. Whisk in milk and cocoa powder until smooth.
  8. Remove from heat and gradually whisk in powdered sugar, vanilla, and salt until the frosting is smooth and spreadable.
  9. Spread the frosting evenly over the cooled cake. Let set for 30 minutes before slicing and serving.

Notes

For an even richer chocolate flavor, use high-quality dark cocoa powder. The boiling water helps bloom the cocoa, intensifying its flavor and creating that signature moist crumb texture. This cake tastes even better the next day as the flavors have more time to develop.