01 - Preheat oven to 350°F. Grease a 9x5-inch loaf pan and line with parchment paper for easy removal.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Pour in melted butter and stir with fork until mixture forms coarse crumbs. Set aside.
03 - In a medium bowl, whisk together 1 1/2 cups flour, baking powder, baking soda, and 1/4 teaspoon salt until well blended.
04 - In a large bowl, beat softened butter and granulated sugar with electric mixer on medium speed until light and fluffy, approximately 3 minutes.
05 - Add eggs one at a time, beating thoroughly after each addition. Mix in lemon zest, lemon juice, sour cream, and vanilla extract until smooth and creamy.
06 - Gradually fold dry ingredients into wet mixture, stirring until just incorporated. Take care not to overmix to maintain tender texture.
07 - Toss blueberries with 1 tablespoon flour to prevent sinking. Gently fold floured berries into batter using rubber spatula until evenly distributed.
08 - Spread batter into prepared pan and level surface. Sprinkle streusel topping evenly over batter. Bake for 50 to 60 minutes until toothpick inserted in center emerges clean.
09 - Allow bread to rest in pan for 15 minutes before removing. Transfer to wire rack and cool completely before slicing into 10 portions.