Lemon Blueberry Sourdough Squares (Print Version)

Moist lemon and blueberry sourdough squares with a crunchy streusel topping; ideal for breakfast or snack.

# 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, active or discard
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 - 1.5 cups fresh blueberries or frozen, 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

# Steps to Follow:

01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, allowing overhang for easy removal.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Add cold diced butter and rub between fingertips until mixture resembles pea-sized crumbs. Refrigerate until needed.
03 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
04 - In a large bowl, cream softened butter and sugar until light and fluffy, approximately 2 to 3 minutes. Add eggs one at a time, beating well after each addition.
05 - Stir in sourdough starter, milk, lemon zest, lemon juice, and vanilla until combined. The mixture may appear slightly curdled.
06 - Add the dry ingredients to the wet ingredients and mix until just combined. Do not overmix.
07 - Gently fold blueberries into batter using a rubber spatula.
08 - Spread batter evenly into the prepared pan. Sprinkle streusel topping evenly across the surface.
09 - Bake for 35 to 40 minutes until a toothpick inserted into the center emerges clean and the top is golden brown.
10 - Allow cake to cool in pan for 15 minutes. Lift out using parchment overhang and transfer to wire rack to cool completely before slicing into squares.

# Additional Tips::

01 -
  • The sourdough starter adds a gentle tang that makes these squares taste less one-dimensional than typical coffee cakes.
  • Fresh blueberries burst with juice while the streusel gives you that satisfying crunch on every bite.
  • They stay moist for days and actually taste better on the second day as flavors deepen.
02 -
  • If you thaw frozen blueberries, they'll release all their color into the batter and turn the cake an unappetizing gray, so resist the urge.
  • The sourdough starter really does make a difference, but if you don't have any active starter, you can use discard starter that's been sitting in your fridge for weeks.
03 -
  • Make the streusel topping while the oven preheats and keep it in the fridge so it stays cold and becomes genuinely crunchy when baked.
  • Room temperature eggs and softened butter make a real difference in how smoothly everything combines, so pull them out about an hour before baking.
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