# Components:
→ Dough
01 - 2 3/4 cups bread flour
02 - 1/3 cup active sourdough starter
03 - 1/4 cup granulated sugar
04 - 1 large egg
05 - 1/2 cup whole milk, lukewarm
06 - 1/4 cup unsalted butter, softened
07 - 1 teaspoon fine sea salt
08 - Zest of 1 large lemon
→ Blueberry Swirl
09 - 1 1/2 cups fresh or frozen blueberries
10 - 1/4 cup granulated sugar
11 - 1 tablespoon lemon juice
12 - 1 tablespoon cornstarch
→ Crumble Topping
13 - 1/3 cup all-purpose flour
14 - 2 tablespoons unsalted butter, cold and cubed
15 - 2 tablespoons light brown sugar
16 - Pinch of salt
# Directions:
01 - In a stand mixer bowl, combine bread flour, granulated sugar, salt, and lemon zest.
02 - Add the sourdough starter, egg, and lukewarm milk to the dry mixture. Mix on low speed to form a shaggy dough.
03 - With the mixer on low speed, add softened butter in small pieces, mixing until fully incorporated and dough becomes smooth and elastic, approximately 8 to 10 minutes.
04 - Place dough in a lightly greased bowl, cover with a damp cloth, and let rise in a warm place until doubled in volume, about 2 hours.
05 - In a small saucepan, combine blueberries, sugar, and lemon juice. Cook over medium heat until berries burst, approximately 5 minutes. Stir in cornstarch and simmer until thickened, 2 to 3 minutes. Cool completely before using.
06 - In a mixing bowl, combine all-purpose flour, light brown sugar, and salt. Cut in cold butter using a pastry cutter or fork until the mixture resembles coarse breadcrumbs. Refrigerate until ready to use.
07 - Once dough has risen, punch down gently and roll out on a lightly floured surface to a 10 by 14-inch rectangle.
08 - Spread the cooled blueberry mixture evenly over the dough, leaving a 1-inch border on all sides.
09 - Roll up the dough tightly from the short side to form a compact log. Place seam-side down in a greased 9 by 5-inch loaf pan.
10 - Cover the loaf pan with a damp cloth and let rise until the dough is puffy and reaches the top of the pan, about 1 hour.
11 - Preheat oven to 350°F. Optionally brush loaf with milk or beaten egg, then sprinkle crumble topping evenly over the surface. Bake for 50 to 55 minutes, tenting with aluminum foil after 30 minutes if browning too quickly.
12 - Cool loaf in the pan for 15 minutes, then transfer to a wire cooling rack to cool completely before slicing.