# What You'll Need:
→ 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
# How-To Steps:
01 - In a stand mixer bowl, combine bread flour, sugar, salt, and lemon zest.
02 - Add the sourdough starter, egg, and lukewarm milk. Mix to form a shaggy dough.
03 - With the mixer on low speed, add softened butter in pieces, mixing until fully incorporated and dough is smooth and elastic, approximately 8 to 10 minutes.
04 - Place dough in a lightly greased bowl, cover, and let rise in a warm place until doubled in size, approximately 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.
06 - Mix flour, brown sugar, and salt in a bowl. Cut in cold butter until the mixture resembles coarse crumbs. Chill until needed.
07 - Once dough has risen, punch down and roll out on a floured surface to a 10 by 14 inch rectangle.
08 - Spread cooled blueberry mixture over the dough, leaving a 1 inch border.
09 - Roll up tightly from the short side to form a log. Place seam-side down in a greased 9 by 5 inch loaf pan.
10 - Cover and let rise until puffy, approximately 1 hour.
11 - Preheat oven to 350°F. Brush loaf with milk or beaten egg if desired, and sprinkle evenly with crumble topping.
12 - Bake for 50 to 55 minutes, tenting with foil after 30 minutes if browning too quickly.
13 - Cool in pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.
