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Easy Chocolate Traybake Recipe: Simple One Pan Chocolate Slab Cake

This easy chocolate traybake recipe creates a moist chocolate sponge cake with rich fudgy icing, perfect for feeding crowds or serving as perfectly portioned slices. It's incredibly versatile - equally delicious as a quick chocolate sponge for everyday enjoyment or dressed up with festive toppings for special occasions.
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Prep Time 20 minutes
Cook Time 35 minutes
Total Time 1 hour 15 minutes
Servings: 12 servings
Calories: 420
Ingredients Method Notes

Ingredients
  

Ingredients
  • 2 cups all-purpose flour
  • 1 ¾ cups granulated sugar
  • ¾ cup unsweetened cocoa powder
  • 1 ½ teaspoons baking powder
  • 1 ½ teaspoons baking soda
  • 1 teaspoon salt
  • 2 large eggs
  • 1 cup whole milk
  • ½ cup vegetable oil
  • 2 teaspoons vanilla extract
  • 1 cup boiling water
  • ½ cup unsalted butter, softened
  • ⅔ cup unsweetened cocoa powder
  • 3 cups powdered sugar
  • ⅓ cup milk
  • 1 teaspoon vanilla extract

Method
 

Instructions
  1. Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan and line it with parchment paper, leaving some overhang for easy removal.
  2. In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
  3. In a separate bowl, beat the eggs, then add the milk, vegetable oil, and vanilla extract. Mix until smooth.
  4. Pour the wet ingredients into the dry ingredients and mix on medium speed until just combined. The batter will be thick.
  5. Carefully stir in the boiling water until the batter is smooth. The batter will be thin - this is normal and creates the moist texture.
  6. Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
  7. Allow the cake to cool in the pan for 10 minutes, then use the parchment paper to lift it onto a wire rack to cool completely before frosting.
  8. Beat the softened butter until creamy. Add cocoa powder and mix until smooth. Gradually add powdered sugar, alternating with milk, beating well after each addition. Stir in vanilla extract until icing is smooth and spreadable.
  9. Spread the fudgy icing evenly over the cooled cake. Cut into squares and serve. This cake keeps well covered at room temperature for up to 3 days.

Notes

Measure flour accurately by spooning into measuring cup and leveling off. Use room temperature ingredients for better incorporation. Don't overmix the batter. Cool cake completely before icing for best results. Cake can be made 2 days ahead and stored at room temperature.