01 - Preheat the oven to 350°F. Grease and flour a 9x5-inch loaf pan or line with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
03 - In a large bowl, beat the softened butter and sugar until light and fluffy, about 2–3 minutes.
04 - Add eggs one at a time, mixing well after each addition. Stir in lemon zest, lemon juice, and vanilla extract.
05 - Add half of the flour mixture to the wet ingredients, mixing gently. Pour in the milk, mix, then add the remaining flour mixture. Stir just until combined—do not overmix.
06 - In a small bowl, toss blueberries with 1 tablespoon flour to prevent sinking. Gently fold blueberries into the batter.
07 - Pour the batter into the prepared loaf pan and smooth the top.
08 - In a small bowl, combine flour, sugar, and cinnamon. Cut in the cold butter until the mixture resembles coarse crumbs. Sprinkle evenly over the batter.
09 - Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean. If the streusel begins to brown too quickly, loosely tent with foil.
10 - Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.