01 - Preheat oven to 350°F. Grease a 9x5-inch loaf pan and line with parchment paper, allowing overhang for easy removal.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Pour melted butter over mixture and stir with fork until coarse crumbs form. Set aside.
03 - In a medium bowl, whisk together flour, baking powder, baking soda, and 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. Stir in lemon zest, lemon juice, sour cream, and vanilla extract until smooth.
06 - Gradually add dry ingredients to wet mixture, mixing by hand with spatula until just combined. Avoid overmixing to prevent tough texture.
07 - Toss blueberries with 1 tablespoon flour in a separate bowl. Gently fold coated berries into batter.
08 - Transfer batter to prepared pan, spreading evenly. Sprinkle streusel topping over surface. Bake for 50 to 60 minutes until wooden pick inserted in center comes out clean.
09 - Let bread cool in pan for 15 minutes. Using parchment overhang, remove to wire rack and cool completely before slicing.