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a piece of vegan sheet cake with wacky cake frosting

Wacky Chocolate Cake

This super moist vegan sheet cake is so easy – its made in the same pan you bake it in! It’s topped with a smooth fudgy buttercream for extra chocolatey-ness.
5 from 2 votes
Prep Time 15 mins
Bake Time 25 mins
Total Time 40 mins
Course Dessert
Cuisine American
Servings 9 slices
Calories 350 kcal


Wacky Chocolate Cake

  • 1⅓ cup +2 tbsp all-purpose flour (200 g)
  • ¾ cup granulated sugar (170 g)
  • ¼ cup cocoa powder (25 g)
  • ¾ tsp salt
  • 1 tsp baking soda
  • 1 tsp baking powder
  • 1 tbsp white vinegar
  • cup canola oil (or other neutral oil) (70 ml)
  • 1 cup cold water (235 ml)

Wacky Cake Frosting (Fudgy Buttercream)

  • ½ cup butter (vegan or regular)
  • ¼ cup vegetable shortening
  • ½ cup cocoa powder
  • cup powdered sugar
  • ½ tsp vanilla extract
  • 1-1½ tbsp milk of choice (if needed)


Wacky Chocolate Cake

  • Preheat oven to 350F.
  • In an un-greased 8x8 square baking pan, add the flour, sugar, cocoa powder, salt, baking soda, and baking powder and mix with a fork until any clumps are gone.
  • With a fork or spoon, make 3 wells in the dry mixture and evenly distribute the oil and vinegar between the them. 
  • Pour the water over the entire mixture and mix with a fork until fully combined, making sure to scoop the corners to get any remaining dry ingredients.
  • Bake for 22-26 minutes or until a toothpick inserted in the middle of the cake comes out clean. Do not over-bake! After 22 minutes, check the cake every 1 minute. If you over-bake, the cake will be dry!
  • Allow the cake to cool completely before frosting.

Wacky Cake Frosting (Fudgy Buttercream)

  • With a standing or electric mixer, whip together the butter and shortening until smooth.
  • Mix in the powdered sugar, then the cocoa powder until well combined.
  • Add in the vanilla, followed by the milk. If the buttercream appears too thick, mix milk in a ½ tbsp at a time until it reaches the desired consistency. If it’s still too thick, add another ½ tbsp of milk.
  • Once the cake has cooled completely, spread the icing on the cake using a spatula.
  • It’s ready to eat! Slice smaller pieces if desired. Store leftovers in an airtight container on the counter or in the fridge.


DOUBLING INSTRUCTIONS: You can easily double this recipe and make it in a 9x13 inch pan. Simply double all ingredient amounts and bake for around 25-35 minutes, or until a toothpick inserted in the middle comes out clean. You can also double the recipe using two 9 inch round cake pans.
STORAGE INSTRUCTIONS: Store the cake in an airtight container or tightly covered at room temperature for up to 4 days. Leftover buttercream can be frozen for up to 2 months in a sealed container.


Calories: 350kcal
Keyword Dairy Free, Vegan
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