01 - Preheat the oven to 350°F. Grease and flour a 9x5-inch loaf pan or line with parchment paper.
02 - Combine flour, sugar, lemon zest, and cold butter. Use fingers or a pastry cutter to blend until coarse crumbs form. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
04 - In a large bowl, beat softened butter and sugar until light and fluffy, about 2-3 minutes. Add eggs one at a time, mixing well after each.
05 - Blend in milk, lemon juice, lemon zest, and vanilla extract until just combined; mixture may appear slightly curdled.
06 - Gradually add dry ingredients to wet ingredients, mixing gently until just incorporated.
07 - Fold in blueberries carefully to avoid breaking them.
08 - Pour batter into prepared pan and smooth the surface. Evenly sprinkle streusel topping over the batter.
09 - Bake for 50-55 minutes until a toothpick inserted into the center comes out clean. Tent loosely with foil if browning too fast during the last 15 minutes.
10 - Let cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.