This recipe is a great way to use some of the zucchini that’s so prolific this time of year (and to hide some fibrous veggies from your family), but fair warning that although it may appear to be a humble sheet cake and therefore easy, it’s actually a labor of love.
You’ll need to carve out time to grate the zucchini fresh, allow an hour for cooling time so the frosting doesn’t melt when you apply it to the cake, brew some hot coffee for the batter (pour yourself a cup at the same time, of course) and make the fluffy frosting from scratch, so I’d recommend saving it for a fun and rewarding project on a rainy August weekend.
The result is so tender, moist and decadent, you’d never know it’s gluten-free and vegan. I slightly modified this recipe by The Banana Diaries, an excellent resource for amazing allergen-free dessert recipes.
Didn’t know you could make vegan buttermilk from oat milk and apple cider vinegar? For more genius, allergen-free ingredient substitutions, subscribe to my weekly emails and I’ll send you an adorable, printable ingredients substitutions chart.
- 9×13" glass baking dish
- Parchment paper
- Small glass mixing bowl or measuring cup
- Large mixing bowl
- Silicone spatula
- 1 ¼ cup oat milk
- 1 tbsp apple cider vinegar
- 1 cup grated zucchini (measure when first grated, then squeeze out as much liquid as possible)
- ½ cup vegan, soy-free, nut-free butter, such as Soy-Free Earth Balance, melted in the microwave and brought to room temperature
- 1 ¾ cups sugar
- ½ cup packed brown sugar
- ¾ cup vegan, nut-free plain, unsweetened yogurt, such as Oatly
- 3 cups gluten-free one-to-one baking flour (such as Bob's Red Mill)
- 1 cup unsweetened cocoa powder
- 2 tsp baking powder
- 1 tsp baking soda
- 1 cup hot coffee
For the Frosting:
- ½ cup room temperature vegan, soy-free, nut-free butter, such as Soy-Free Earth Balance
- ¼ cup room temperature vegan, nut-free sour cream
- 1 cup vegan dark chocolate chips, such as Enjoy Life, plus more for topping
- 1 tbsp coconut oil
- 4-6 cups powdered sugar
- ¼ cup cocoa powder
- extra oat milk for thinning out the frosting if needed
- Preheat the oven to 350 degrees F.
- Line the glass baking dish with parchment paper.
- Make the vegan buttermilk: In a glass bowl, combine 1 1/4 cups oat milk and 1 tbsp apple cider vinegar and allow to sit at room temperature (mixture will curdle a bit and this is normal).
- Grate zucchini and squeeze out as much liquid as possible.
- In a large mixing bowl, whisk together melted vegan butter, sugar, brown sugar and vegan yogurt.
- Add zucchini and stir until combined.
- Sift in flour, cocoa powder, baking powder and baking soda (do not mix yet).
- Add vegan buttermilk mixture and whisk. Before dry ingredients are fully incorporated, add hot coffee and fold batter with a silicone spatula or spoon until just incorporated – do not over mix (the batter will be a bit slippery and slimy; this is normal).
- Pour the batter into the prepared baking dish and place in the oven for about 40 minutes or until a toothpick inserted into the center of the cake comes out clean.
- Remove cake from oven and allow to cook completely for about 1 hour.
- When you're ready to assemble the cake, remove the butter and sour cream from the refrigerator and allow to come to room temperature.
- Make the frosting: Using a hand mixer, cream together ½ cup vegan butter until fluffy (about 3 minutes).
- Add sour cream to butter and mix again.
- Place the vegan chocolate chips and coconut oil into a small glass bowl and microwave in 30-second increments, stirring in between each time, until chocolate is melted and smooth. Allow it to come to room temperature.
- Pour the chocolate mixture into the butter and sour cream mixture. Mix until smooth.
- Add powdered sugar in 2-cup increments until a frosting consistency is reached, then add cocoa powder and mix until fluffy.
- If frosting becomes too stiff, add a bit of oat milk in 1 tbsp increments.
- Frost the cake, top with more vegan chocolate chips if desired, and serve!
- Leftovers can be stored in an airtight container for up to 3 days.