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freshly made and decorated sourdough American flag cake

Sourdough American Flag Cake

Molly LaFontaine
My sourdough American flag cake is made with from-scratch sourdough lemon sheet cake, homemade whipped cream frosting, and decorated with fresh berries. It's moist, light, and refreshing, making it the perfect 4th of July cake or summer dessert!
Prep Time 25 minutes
Cook Time 22 minutes
Cake Cooling 45 minutes
Total Time 1 hour 32 minutes
Course Dessert
Cuisine Sourdough
Servings 12 slices (medium sheet cake)

Ingredients
  

Sourdough Lemon Sheet Cake

  • 1/3 cup avocado oil (or coconut oil, not olive oil)
  • 3/4 cup raw cane sugar
  • 2 large eggs
  • 1 tsp pure vanilla extract
  • 1/4 cup sourdough discard (fed starter works too)
  • 3/4 cup milk (I use whole dairy milk)
  • 1/2 cup sour cream (or plain unsweetened yogurt)
  • 1/2 tsp sea salt
  • 2 Tbsp lemon zest, packed into the measuring spoon
  • 1 Tbsp lemon juice (fresh or pure bottled)
  • 2 tsp baking powder (I use aluminum-free)
  • 1/2 tsp baking soda
  • 1 1/2 cup all-purpose flour (I use organic, unbleached)

Whipped Cream Frosting

  • 1 cup heavy whipping cream (I use organic for no additives)
  • 1 tsp pure vanilla extract
  • 2 Tbsp raw cane sugar
  • 2 oz plain cream cheese

Decorations

  • 1 cup blueberries about 1/2 pint
  • 2 cups raspberries about 1-2 pints

Instructions
 

  • Preheat oven to 350 degrees Fahrenheit, get cream cheese out of fridge so it can warm for the frosting, and butter/flour a medium stainless steel rimmed sheet pan (approximately 12”x 9”). Set aside.

Make the Batter

  • In a large mixing bowl add avocado oil and sugar. Mix with an electric mixer on low speed for 2 minutes.
  • Add eggs one at a time. Mix each into the mixture on low speed until completely combined both times.
  • Add in vanilla, sourdough discard, milk, sour cream, salt, lemon zest, lemon juice, baking powder, and baking soda (wait to add baking powder and baking soda if you’re doing the optional cold ferment step below). Mix on low-medium speed until everything is combined and no clumps are left, about 30 seconds.
  • Add in flour and mix on medium speed JUST UNTIL combined. Do not over mix.
  • Optional – At this point you can either continue the recipe or place the batter in the fridge, covered, for 12-24 hours to ferment for more sourdough fermentation benefits. When you’re ready to continue the recipe stir in the baking powder and baking soda just before baking. This may make the cake a little more dense.
  • Pour cake batter into the greased sheet pan. Spread evenly with a spatula to fill the entire pan.

Bake & Cool

  • Bake for 22-24 minutes or until fully baked, avoid over-baking (if your pan is a different size bake time can vary).
  • When cake is baked completely a toothpick should come out clean and the center should look set. Take cake out of the oven and let cool in the pan for 15-20 minutes.
  • After slightly cooled, use a spatula to loosen the edges all around the cake.
  • Place a piece of parchment paper on top then use hot pads to flip the pan so the parchment paper is now on the cooling rack with the pan bottom facing up. Tap the bottom of the pan to help loosen the cake and gently remove pan off the top. The cake should come right out. If it doesn’t, use your fingers to get an edge started. Let cool completely before frosting.

Make the Frosting

  • While the cake cools, in a medium sized mixing bowl, add cold heavy whipping cream, vanilla extract, cane sugar, and softened cream cheese.
  • Use an electric mixer on medium speed to whip the ingredients together for 2-5 minutes until stiff peaks form (this means the whipped cream stays on the whisk and doesn’t drop off). Please be patient, it takes a little bit to thicken especially if you’re using organic heavy whipping cream. When it’s done set it in the fridge until the cake cools completely.

Decorate the Cake

  • Once cake is cooled, add all the whipped cream frosting to the top and spread with a butter knife to evenly coat the entire top, leave sides bare.
  • Rinse blueberries and raspberries with water and dry with a kitchen towel. Add blueberries in a rectangle to the top left of the cake for the blue star area. Place blueberries close together in the rectangle.
  • Add raspberries to make the stripes, I do 4 starting with one at the top, two in the middle, and one at the bottom of the cake. Stagger the raspberries so that the top of one raspberry is beside the bottom of the other, it makes a more solid stripe.
  • Use a butter knife to make a textured white stripe in the frosting between the rows of berries going horizontally across the cake.
  • This cake is best enjoyed immedietly but will last up to 3 days in the fridge. Store in an airtight container to prevent excessive drying out.

Notes

  • I don't recommend making the frosting too far ahead, it's best fresh.
  • Heavy whipping cream must be cold, right out of the fridge, to make the frosting
Did you make this recipe? – If you loved it, I'd be so grateful if you left a comment on the blog post. It helps more than you know. You can share a photo on social media, tag @plumbranchhome
 
Sourdough Baking Disclaimer – I regularly feed my sourdough starter a 2:1 ratio of unbleached flour to filtered water, this creates a 50% hydrated starter even when I use discard. If you feed your starter differently, results may vary due to a different hydration which will cause a different consistency. No matter how you feed your starter just ensure it’s a thick consistency when you use it for my recipes, even if you’re using discard.
 
A Note From Molly – I NEVER use AI (artificial intelligence) to develop recipes or create content for plumbranchhome.com. What you see from PBH is real, made for a reason, tested, and loved.
 
Here at Plum Branch Home we’re serving God by loving our families one simple, wholesome, made from scratch recipe at a time!
Keyword sourdough american flag cake