Lemon Blueberry Sourdough Squares (Printable version)

Tangy lemon and juicy blueberries combine with sourdough and streusel for a moist, flavorful treat.

# What You'll Need:

→ Cake Batter

01 - 1/2 cup unsalted butter, softened
02 - 3/4 cup granulated sugar
03 - 2 large eggs
04 - 1/2 cup sourdough starter, discard or active unfed
05 - 1 cup whole milk
06 - Zest of 1 lemon
07 - 2 tablespoons fresh lemon juice
08 - 1 teaspoon vanilla extract
09 - 2 cups all-purpose flour
10 - 2 teaspoons baking powder
11 - 1/2 teaspoon baking soda
12 - 1/2 teaspoon fine sea salt
13 - 1 1/2 cups fresh or frozen blueberries, unthawed

→ Streusel Topping

14 - 1/4 cup unsalted butter, cold and diced
15 - 1/3 cup light brown sugar, packed
16 - 1/2 cup all-purpose flour
17 - 1/2 teaspoon ground cinnamon
18 - Pinch of salt

# Directions:

01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Add cold diced butter and rub with fingertips until mixture forms pea-sized crumbs. Refrigerate until needed.
03 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
04 - In a large bowl, cream butter and sugar until light and fluffy, approximately 2-3 minutes. Beat in eggs one at a time.
05 - Stir in sourdough starter, milk, lemon zest, lemon juice, and vanilla until combined. The mixture may appear slightly curdled.
06 - Add dry ingredients to wet ingredients and mix until just combined.
07 - Gently fold blueberries into batter.
08 - Spread batter evenly into prepared pan. Sprinkle streusel topping evenly over batter.
09 - Bake for 35-40 minutes until a toothpick inserted into center comes out clean and top is golden brown.
10 - Cool in pan for 15 minutes, then lift out using parchment overhang and cool completely on wire rack before slicing into squares.

# Expert Advice:

01 -
  • Uses sourdough discard to reduce waste while adding depth of flavor
  • Bright lemon zest and juice create a refreshing citrus note
  • Crunchy streusel topping provides textural contrast to the moist cake
  • Easy to slice into portable squares perfect for sharing
  • Freezes beautifully for make-ahead convenience
02 -
  • Room temperature ingredients mix more evenly—take eggs and butter out 30 minutes before baking
  • Don't overmix the batter once flour is added to keep the cake tender
  • Test doneness with a toothpick in the center; a few moist crumbs are fine but wet batter means it needs more time
  • The parchment paper overhang makes removing the cake from the pan effortless
  • For the crumbliest streusel, keep the butter very cold and work quickly
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