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Sourdough Banana Cake with Brown Butter Frosting

If you’re looking for a way to use up ripe bananas and your sourdough discard, this fluffy banana cake is it. It’s soft and light—more like a banana sheet cake than banana bread—and topped with the dreamiest whipped brown butter cream cheese frosting that tastes like salted caramel cheesecake.
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Prep Time 10 minutes
Cook Time 40 minutes
30 minutes
Total Time 1 hour 20 minutes
Servings: 12
Course: Dessert, sourdough
Ingredients Equipment Method

Ingredients
  

For the Banana Cake:
  • 3 Overripe Bananas (1 cup mashed): The riper the better! They add natural sweetness and moisture while helping create a tender crumb.
  • 1/2 cup Sourdough starter discard: Adds subtle tang and helps keep the cake moist. Bonus points for reducing food waste! Don’t worry—it won’t taste “sour.”
  • 2 Eggs: Eggs provide structure and help the cake rise. Room temperature eggs work best for a smooth batter.
  • 3/4 cups Granulated Sugar: Gives sweetness and balances the banana flavor.
  • 1/4 cup Brown Sugar: Adds warmth and depth. The molasses in brown sugar complements the banana beautifully.
  • 1/2 cup Neutral Oil: Keeps the cake super moist without weighing it down. I love using avocado oil, but vegetable or canola work too.
  • 1/2 cup Milk: Loosens the batter and adds moisture. Buttermilk also works and adds even more tenderness.
  • 1 tsp Vanilla Extract: Enhances all the other flavors.
  • 1 3/4 cups All-Purpose Flour: Just the right amount for structure without making the cake dense.
  • 1 tsp Baking Powder: These leaveners work together to help the cake rise. The soda reacts with the acidity of the sourdough and bananas.
  • 1/2 tsp Baking Soda
  • 1/2 tsp Salt: A little salt brings out the sweetness and balances the flavors.
  • 1/2 tsp Cinnamon: Warm spice notes that go beautifully with banana and brown sugar. I always add it.
Whipped Brown Butter Cream Cheese Frosting
  • 1/2 cup unsalted butter
  • 3/4 cup cup brown sugar
  • 2 tbl  heavy cream
  • 1/2 tsp salt
  • 8 oz cream cheese, softened
  • 1/2 cup powdered sugar, sifted
  • 1 tsp vanilla extract

Equipment

  • Mixing bowls (1 large, 1 medium) – for wet and dry ingredients
  • Whisk – to mix the batter smoothly
  • Rubber spatula or wooden spoon – for folding the batter
  • Measuring cups and spoons – essential for accurate baking
  • 9x13-inch baking pan
  • Parchment paper – for easy removal and clean edges
  • Oven mitts – safety first!
  • Small saucepan – to brown the butter and melt the brown sugar
  • Hand mixer or stand mixer – for whipping cream cheese and frosting

Method
 

Preheat the Oven
  1. Set your oven to 350°F (175°C). Grease and line a 9×13-inch cake pan or two 8-inch round cake pans with parchment paper.
Make the Cake Batter
  1. In a large bowl, whisk together mashed bananas, sourdough discard, eggs, white sugar, brown sugar, oil, milk, and vanilla extract until smooth.
    In a separate bowl, combine the flour, baking powder, baking soda, salt, and cinnamon. Whisk to distribute evenly.
    Add the dry ingredients into the wet ingredients and stir until just combined. Don’t overmix—stop as soon as the flour disappears to keep the crumb light.
Bake
  1. Pour the batter into your prepared pan. Bake for 35–40 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. Let the cake cool completely before frosting.
Whipped Brown Butter Cream Cheese Frosting
  1. Brown the Butter: In a saucepan, melt the butter over medium heat until it foams and smells nutty, and the solids at the bottom turn golden brown. Don’t walk away, the butter may burn too quickly.
  2. Make Caramel Base: Add brown sugar, heavy cream, and salt to the browned butter. Simmer gently for 1–2 minutes, or until the sugar has dissolved. Remove from heat.
  3. Cool It Down: Let this mixture cool to room temperature—it should still be soft but no longer warm.
  4. Cream the Cheese: Beat the softened cream cheese in a bowl until smooth and fluffy.
  5. Combine & Whip: Slowly add the cooled brown butter mixture to the cream cheese. Using a hand mixer mix until smooth, then beat in powdered sugar and vanilla until fluffy and well combined.
  6. Frost the Cake: Once the cake is fully cooled, spread or pipe this luscious frosting over the top. It will set up slightly as it rests.