Let's Bake

Chocolate Sheet Cake

Yield Makes 20-24 slices 1x
Prep: 60 minutesCook: 35 minutesTotal: 1 hour 35 minutes

Large Chocolate Sheet Cake covered in chocolate frosting and candy. 


Chocolate cake

  • 120 ml (1/2 cup) hot water
  • 230 grams (1 cup) unsalted butter, room temperature
  • 200 grams (1 cup) caster sugar or granulated sugar
  • 90 grams (1/2 cup) brown sugar
  • 2 teaspoons vanilla extract
  • 3 large eggs, room temperature
  • 245 grams (1 and 3/4 cup) plain flour or all purpose flour
  • 60 grams (3/4 cup) cocoa powder
  • 1 teaspoon baking powder
  • 1 teaspoon baking soda
  • 1/2 teaspoon salt
  • 240 ml (1 cup) full fat sour cream, room temperature

Chocolate frosting

  • 115 grams (1/2 cup or 1 stick) unsalted butter, room temperature
  • 75 grams (1/2 cups) dark chocolate (50-70% cocoa), roughly chopped
  • 250 grams (2 cups) icing sugar or powdered sugar, sifted
  • 3 tablespoons full fat sour cream, room temperature
  • 450 grams (3 cups) assorted chocolate and candy pieces, roughly chopped


  1. Chocolate cake
    Grease a quarter-sized sheet pan (9 x 13 inch / 23 x 33 cm) and line with baking or parchment paper, ensuring two sides of the paper overhang.
  2. Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Boil the kettle and pour out 1/2 cup water and set aside.
  3. In a large mixing bowl, beat butter and sugars with an electric mixer on medium speed for 1-2 minutes or until creamy and combined.
  4. Add vanilla and eggs, one at a time, and continue to beat until combined. Take a moment to scrape down the sides of the bowl. 
  5. In a separate bowl, sift flour, cocoa powder, baking powder, baking soda and salt and lightly whisk. Add the dry ingredients, along with the hot water and gently mix on low speed.
  6. Add sour cream and mix on low speed until cake batter is smooth and creamy. 
  7. Pour chocolate batter into your prepared pan and smooth out into one even layer.
  8. Bake for approximately 35 minutes or until a skewer inserted into the middle of the cake comes out clean. Leave the cake to cool for about 15 minutes before carefully transferring to a wire rack to cool completely.
  9. Chocolate frosting
    Place butter in a large mixing bowl and beat with an electric mixer on medium speed until pale and creamy.
  10. Meanwhile, melt chocolate in the microwave, stirring every 20 second, until smooth and set aside to cool slightly.
  11. Add half the sugar and the sour cream, and beat on low until the sugar is incorporated. Then, add the remaining sugar and beat on low until mixture is smooth and creamy.
  12. Next, add melted chocolate to the buttercream, ensuring the chocolate is still smooth and melted but not warm. Beat on medium speed until chocolate buttercream is smooth and creamy. 
  13. Gently cover your cooled cake with chocolate frosting. Then scatter candy pieces on top.


Cocoa powder: Use unsweetened 100% cocoa powder for this recipe. 

Sour cream: I recommend using full fat sour cream for both the cake and the chocolate frosting. If you don’t have access to sour cream, you can use full fat Greek yogurt instead. 

Dark chocolate: Use a good quality dark chocolate for the frosting, somewhere between 50-70% cocoa. 

Candy: You can use any chocolate or candy you like to decorate this cake. I used M&M’s, Maltesers, Twix bars and Snickers bars.

Make-ahead: You can make the chocolate frosting ahead of time and store it covered in an airtight container in the fridge. When you’re ready to use it, leave it to thaw at room temperature for 30 minutes. Then, add a dash of milk as needed and mix it on low speed using an electric mixer until it becomes smooth and creamy again. 

Storage: Once the cake is frosted, you’ll need to store it in the fridge. I recommend bringing the cake back to room temperature before serving. Alternatively, you can store the cake itself at room temperature in an airtight container and just frost it when you’re ready to serve. 

Cake pan: This recipe will make enough cake batter to make a 9 by 13 inch cake, or you can make a two layer 8-inch cake or a three layer 6-inch cake.  

Nutrition Information

Serving Size: 1 slice Calories: 373 Sugar: 33.9 g Sodium: 148.2 mg Fat: 20.1 g Carbohydrates: 46.4 g Protein: 3.9 g Cholesterol: 62.1 mg
Nutrition information is a guide only.
Author: Jessica HolmesCategory: CakeCuisine: Dessert
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