Rich Sourdough Zucchini Brownies

Here are my sourdough zucchini brownies, with rich cocoa powder, melted butter, shredded zucchini, and tons of chocolate chips mixed into a fudgy batter made extra special with tangy sourdough starter.

These brownies are my go-to recipe when my garden is overflowing with zucchini in the summer. The sourdough starter gives them a slight tang that balances out the sweetness, and nobody ever guesses there’s three whole cups of vegetables hidden inside. Perfect for using up that extra starter and sneaking some veggies into dessert!

What Kind of Zucchini Should I Use?

Any type of zucchini will work great in these brownies, whether you’ve got dark green, light green, or even yellow summer squash from your garden. Medium-sized zucchini tend to be the best choice since they’re tender and have fewer seeds than the giant ones that got away from you in the garden. When you’re shredding your zucchini, don’t worry about squeezing out the moisture – you’ll actually want to keep all that liquid in since it helps make the brownies super moist and fudgy. If your zucchini has a really thick skin or large seeds, you might want to peel it or scoop out the seeds, but for most regular-sized zucchini, you can just shred the whole thing.

Options for Substitutions

Here are some swaps you can make if you need to work with what you have:

• Sourdough starter: This is what makes these brownies special, so I wouldn’t skip it. Both active starter and discard work perfectly fine here – no need to wait for it to be bubbly.
• Butter: You can use coconut oil or vegetable oil instead of butter. The texture will be slightly different but still good – just make sure it’s melted and cooled a bit before mixing.
• Sugar: White sugar works best here, but you can replace up to half of it with brown sugar for a deeper flavor. I wouldn’t recommend using all brown sugar as it might make the brownies too dense.
• Zucchini: Yellow squash can work in place of zucchini. Just shred it the same way and don’t drain it – that moisture keeps the brownies fudgy.
• Semi-sweet chocolate chips: Dark chocolate chips, milk chocolate chips, or even chopped chocolate bars all work great. You can also mix in some white chocolate chips for variety.
• Eggs: If you’re short one egg, you can use 2 whole eggs instead of 1 egg plus 1 yolk. The brownies might be slightly less rich but will still turn out well.

Watch Out for These Mistakes While Baking

The biggest mistake people make with zucchini brownies is squeezing out the moisture from the shredded zucchini, which actually makes the brownies dry instead of fudgy – leave all that liquid in for the best texture.

Overbaking is another common issue, so pull the brownies out when a toothpick inserted in the center comes out with a few moist crumbs (not completely clean), since they’ll continue cooking as they cool in the pan.

Don’t skip the 10-15 minute rest after mixing the batter, as this allows the sourdough starter to work with the other ingredients and helps create a better crumb structure.

Finally, resist the urge to cut into these brownies while they’re still warm – letting them cool completely makes them much easier to slice cleanly and helps the texture set properly.

What to Serve With Sourdough Zucchini Brownies?

These brownies are pretty rich and fudgy on their own, so they’re perfect with a cold glass of milk or a scoop of vanilla ice cream on top. If you’re serving them for dessert after dinner, a cup of hot coffee or espresso really brings out the chocolate flavor. I love cutting them into squares and packing them up for picnics or potlucks since they travel well and don’t need any fancy plating. For an extra treat, you can warm them up slightly in the microwave and add a dollop of whipped cream or even some fresh berries on the side.

Storage Instructions

Store: Keep these brownies in an airtight container at room temperature for up to 3 days, or in the fridge for up to a week. The zucchini actually helps keep them moist and fudgy, so they taste great even after a few days.

Freeze: These brownies freeze really well for up to 3 months. I like to cut them into individual squares and wrap each one in plastic wrap, then store them all in a freezer bag. That way you can grab just one or two whenever a chocolate craving hits.

Serve: If you’re eating them from the fridge, let them sit at room temperature for about 10 minutes to soften up a bit. Frozen brownies can thaw on the counter in about 30 minutes, or you can microwave them for 15-20 seconds for that warm, gooey brownie experience.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 3300-3600
• Protein: 36-42 g
• Fat: 175-190 g
• Carbohydrates: 420-450 g

Ingredients

For the dry ingredients:

• 1 1/4 cups all-purpose flour
• 2/3 cup cocoa powder (sifted)
• 1 tsp salt
• 1/2 tsp baking soda
• 1/2 tsp espresso powder (optional)

For the batter:

• 1/2 cup plus 1 tablespoon unsalted butter, melted
• 1 1/2 cups sugar
• 1/4 cup sourdough starter
• 1 egg
• 1 egg yolk
• 1 tbsp vanilla extract
• 3 cups shredded zucchini
• 1 1/2 cups semi-sweet chocolate chips
• 1/2 tsp flaky sea salt (for topping)

Step 1: Prepare Pan and Combine Dry Ingredients

• 1 1/4 cups all-purpose flour
• 2/3 cup cocoa powder
• 1 tsp salt
• 1/2 tsp baking soda
• 1/2 tsp espresso powder

Preheat your oven to 325°F and grease a 9×13 inch baking dish or similar size with butter or cooking spray.

While the oven heats, whisk together the flour, sifted cocoa powder, salt, baking soda, and espresso powder (if using) in a medium bowl.

Setting up your mise en place now means you’ll work efficiently once you start mixing the wet ingredients.

Step 2: Build the Wet Ingredient Base

• 1/2 cup plus 1 tablespoon unsalted butter, melted
• 1 1/2 cups sugar
• 1/4 cup sourdough starter
• 1 egg
• 1 egg yolk
• 1 tbsp vanilla extract

In a large bowl, whisk together the melted butter, sugar, sourdough starter, egg, egg yolk, and vanilla extract until well combined and slightly lighter in appearance.

The sourdough starter adds tanginess and depth that enhances the chocolate flavor, so make sure it’s fully incorporated.

This mixture is the foundation for moisture and flavor, so take your time to whisk thoroughly.

Step 3: Combine All Ingredients and Let Rest

• dry ingredient mixture from Step 1
• wet ingredient mixture from Step 2
• 3 cups shredded zucchini
• 1 1/2 cups semi-sweet chocolate chips

Add the dry ingredient mixture from Step 1 to the wet mixture from Step 2, then fold in the shredded zucchini until just combined—don’t overmix, as this can make the brownies tough.

Let the batter rest for 10 to 15 minutes at room temperature; I find this resting period allows the zucchini to release moisture and the cocoa to fully hydrate, which creates a more fudgy texture.

After resting, stir the batter once more and fold in the chocolate chips.

Step 4: Bake and Cool

• batter from Step 3
• 1/2 tsp flaky sea salt

Pour the batter into your prepared baking dish and spread it evenly.

Bake at 325°F for 35 to 42 minutes, until a toothpick inserted into the center comes out with just a few moist crumbs—remember, these are meant to be fudgy, not dry.

Once baked, let the brownies cool completely in the pan before cutting into squares, then sprinkle with flaky sea salt over the top for a subtle contrast to the rich chocolate.

Rich Sourdough Zucchini Brownies

Delicious Rich Sourdough Zucchini Brownies recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 20 minutes mins

Cook Time 45 minutes mins

Total Time 1 hour hr 5 minutes mins

Servings: 18 pieces

Calories: 3450

Ingredients Method

Ingredients

  

For the dry ingredients:

• 1 1/4 cups all-purpose flour
• 2/3 cup cocoa powder (sifted)
• 1 tsp salt
• 1/2 tsp baking soda
• 1/2 tsp espresso powder (optional)

For the batter:

• 1/2 cup plus 1 tablespoon unsalted butter, melted
• 1 1/2 cups sugar
• 1/4 cup sourdough starter
• 1 egg
• 1 egg yolk
• 1 tbsp vanilla extract
• 3 cups shredded zucchini
• 1 1/2 cups semi-sweet chocolate chips
• 1/2 tsp flaky sea salt (for topping)

Method

 

1. Preheat your oven to 325°F and grease a 9x13 inch baking dish or similar size with butter or cooking spray. While the oven heats, whisk together the flour, sifted cocoa powder, salt, baking soda, and espresso powder (if using) in a medium bowl. Setting up your mise en place now means you'll work efficiently once you start mixing the wet ingredients.
2. In a large bowl, whisk together the melted butter, sugar, sourdough starter, egg, egg yolk, and vanilla extract until well combined and slightly lighter in appearance. The sourdough starter adds tanginess and depth that enhances the chocolate flavor, so make sure it's fully incorporated. This mixture is the foundation for moisture and flavor, so take your time to whisk thoroughly.
3. Add the dry ingredient mixture from Step 1 to the wet mixture from Step 2, then fold in the shredded zucchini until just combined—don't overmix, as this can make the brownies tough. Let the batter rest for 10 to 15 minutes at room temperature; I find this resting period allows the zucchini to release moisture and the cocoa to fully hydrate, which creates a more fudgy texture. After resting, stir the batter once more and fold in the chocolate chips.
4. Pour the batter into your prepared baking dish and spread it evenly. Bake at 325°F for 35 to 42 minutes, until a toothpick inserted into the center comes out with just a few moist crumbs—remember, these are meant to be fudgy, not dry. Once baked, let the brownies cool completely in the pan before cutting into squares, then sprinkle with flaky sea salt over the top for a subtle contrast to the rich chocolate.