01 - Preheat the oven to 350°F. Grease and flour a 9x5-inch loaf pan or line it with parchment paper.
02 - Combine flour, sugar, lemon zest, and cold butter in a small bowl. Using fingers or a pastry cutter, blend until the mixture forms coarse crumbs. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
04 - Beat softened butter and sugar in a large bowl until light and fluffy, about 2 to 3 minutes. Add eggs one at a time, beating well after each addition.
05 - Mix in milk, lemon juice, lemon zest, and vanilla extract until just combined; the mixture may appear slightly curdled.
06 - Gradually add the dry flour mixture to the wet ingredients, stirring just until combined.
07 - Gently fold the blueberries into the batter to avoid breaking them.
08 - Pour batter into the prepared loaf pan and smooth the surface. Evenly sprinkle the streusel topping over the batter.
09 - Bake for 50 to 55 minutes, or until a toothpick inserted in the center comes out clean. Tent lightly with foil in the last 15 minutes if the top browns too quickly.
10 - Allow to cool in the pan for 15 minutes before transferring to a wire rack to cool completely before slicing.