Blueberry Lemon Sourdough Cake

There's something magical about the moment when a cast iron skillet emerges from the oven with a golden, billowing cake studded with jewel-toned blueberries. My sourdough starter had been sitting neglected in the fridge for weeks, and I found myself wanting to use it for something other than bread, something that would celebrate its tangy complexity without overpowering the delicate fruit. This skillet cake became that answer, combining the depth of sourdough with bright lemon and plump blueberries in one humble dessert.

I baked this for my neighbor one afternoon when she stopped by with homemade jam, and we ended up sitting on my porch with warm slices, ice cream melting into the cake. She kept asking what made it taste so different from typical lemon cakes, and I realized it was that sourdough undertone, the way it added complexity without announcing itself. It became our shorthand for gatherings after that, the cake I'd reach for when I wanted something that felt both approachable and a little bit special.

Ingredients

• All-purpose flour: This is your structural backbone; measure it by spooning into your cup rather than scooping directly to avoid packing it too tightly.
• Unsalted butter: Softening it at room temperature takes about an hour, but you can quicken the process by cutting it into smaller cubes.
• Granulated sugar: Creaming sugar and butter together incorporates tiny air bubbles that make the cake tender and give it lift.
• Eggs: Room temperature eggs blend more smoothly into the batter; set them out while you're prepping other ingredients.
• Active sourdough starter: This should be the discard you feed but don't use for baking; its slight fermentation adds complexity and keeps the cake moist for days.
• Whole milk: Adds moisture and richness without overshadowing the lemon flavor.
• Vanilla extract: Use pure vanilla if you can; imitation versions can taste bitter when combined with strong lemon notes.
• Lemon zest and juice: Zest the lemon before cutting it in half, and use fresh-squeezed juice if possible; bottled juice tends to taste tinny and sharp.
• Baking powder and baking soda: The baking soda reacts with the acidic sourdough starter and lemon juice to create lift, while baking powder provides additional rise.
• Fresh blueberries: Toss them lightly in a tablespoon of flour before folding in to help them stay suspended and prevent them from sinking.
• Powdered sugar for icing: Sift it if it's lumpy, which it often is after sitting in a humid kitchen.

Instructions

Mount paper towels nearby for quick cleanup of spills, grease, and messes while cooking and prepping meals.

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Heat your oven and prepare the skillet:

Preheat to 350°F and grease your 10-inch skillet generously with butter or nonstick spray, paying extra attention to the corners where batter tends to stick. A well-seasoned cast iron skillet is ideal, but any oven-safe skillet works beautifully.

Mix your dry ingredients:

Whisk flour, baking powder, baking soda, and salt together in a medium bowl and set aside. This ensures the leavening agents are evenly distributed throughout the batter.

Cream butter and sugar:

In a large bowl, beat softened butter and sugar together for about 2 minutes until the mixture looks pale, fluffy, and noticeably lighter in color. This aerates the batter and sets the foundation for a tender crumb.

Add eggs one at a time:

Add each egg individually, mixing well after each addition so it fully incorporates before adding the next. This prevents a curdled-looking batter and helps emulsify the dough.

Brighten with lemon and vanilla:

Stir in vanilla extract, lemon zest, and lemon juice, then fold in the sourdough starter until everything is combined. The batter may look slightly curdled at this point, which is normal and nothing to worry about.

Layer in the flour and milk:

Add half the flour mixture and stir until just incorporated, then pour in the milk, and finish with the remaining flour mixture, stirring gently to avoid overworking the batter. Overmixing develops gluten and creates a dense, tough cake.

Fold in the blueberries:

Using a spatula, gently fold in the blueberries with as few strokes as possible; they should be scattered throughout but not crushed. If using frozen blueberries, add them straight from the freezer without thawing.

Transfer and bake:

Pour the batter into your prepared skillet and spread it evenly with a spatula. Top with a few extra blueberries if you like, and slide the skillet into the preheated oven.

Watch for golden perfection:

Bake for 30 to 35 minutes until the cake is golden brown and a toothpick inserted in the center comes out clean or with just a few moist crumbs. The top should spring back slightly when gently touched.

Cool before icing:

Let the cake cool in the skillet for about 15 minutes; this allows it to set enough to support the icing without falling apart.

Make and drizzle the icing:

Whisk powdered sugar with lemon juice until it reaches a thick but pourable consistency, then drizzle it across the warm cake in thin streams. The icing will set slightly as it cools but remain glossy and delicate.

Save

The first time I served this cake still warm with vanilla ice cream melting into the lemon icing, my partner asked why I didn't make it more often. It's become one of those desserts that feels like a small celebration even on ordinary Tuesdays, a way to use what's already in my sourdough jar and turn it into something that tastes like I spent all day planning it.

Why Sourdough Starter Belongs in Desserts

When most people think of sourdough starter, they picture loaves of bread with that distinctive tangy crumb. But the starter itself is a living culture of wild yeast and beneficial bacteria, and that fermentation magic translates beautifully into cakes, where it adds moisture, complexity, and a subtle flavor that lingers without tasting sour. Using discard starter in baking is also practical; it gives you a reason to keep feeding your jar without feeling wasteful, and the slight acidity helps activate baking soda for reliable rise.

Cast Iron Magic

There's a reason I reach for cast iron for this cake: the skillet heats evenly and retains warmth beautifully, creating a gently caramelized bottom edge while the top stays tender and moist. The iron also conducts heat in a way that ensures the center bakes through without the edges overdrying, and the visual appeal of serving a cake directly from its cooking vessel feels effortless and charming.

Variations and Customizations

This cake welcomes improvisation once you understand how it works. The lemon can be swapped for other citrus like orange or lime, frozen blueberries work just as well as fresh if you add them straight from the freezer without thawing, and a sprinkle of coarse turbinado sugar before baking adds a pleasant textural contrast. Some days I fold in a handful of sliced almonds, and other times I serve it with whipped cream lightly sweetened with a touch of lemon juice.

• Try a mixture of berries (raspberries, blackberries, blueberries) for a more complex berry flavor.
• A drizzle of white chocolate melted with a tiny bit of coconut oil can replace the lemon icing for a richer finish.
• If you don't have sourdough starter, substitute with an extra tablespoon of flour and an additional quarter cup of milk, though you'll lose that subtle tangy depth.

Track cooking times accurately for baking, boiling, roasting, and multitasking recipes without overcooking.

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Save

This cake tastes even better the next day when the sourdough starter has continued its quiet work, making everything taste deeper and more interesting. Wrap leftovers loosely and keep them at room temperature or refrigerate; either way, a slice with morning coffee feels like a small luxury you've already earned.

Kitchen Q&A

→ What gives this cake its tangy flavor?

The zesty lemon juice and lemon zest provide a bright tang, complemented by the natural sourness of the sourdough starter for added depth.

→ Can I use frozen blueberries instead of fresh?

Yes, frozen blueberries can be used directly without thawing to maintain texture and prevent color bleeding.

→ Why use a cast iron skillet for baking?

A cast iron skillet ensures even heat distribution, resulting in a golden crust and consistent bake throughout.

→ How is the icing drizzle made?

The icing combines powdered sugar with fresh lemon juice, whisked to a thick but pourable consistency for drizzling over the cooled cake.

→ Can I substitute sourdough starter with something else?

Sourdough starter adds unique flavor and moisture; a small amount of yogurt or buttermilk can provide similar richness but will slightly change the taste.

→ What variations can I try with this cake?

Try replacing lemon zest and juice with orange for a different citrus profile or sprinkle almonds on top for added crunch before baking.