01 - Preheat the oven to 350°F. Grease and line a 9x5 inch loaf pan with parchment paper.
02 - Combine flour, brown sugar, cinnamon, and salt in a bowl. Add cold butter and blend with a pastry cutter or fingers until crumbly. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a separate bowl; set aside.
04 - Beat softened butter and granulated sugar until light and fluffy, about 2 to 3 minutes.
05 - Incorporate eggs one at a time, beating well after each addition. Then mix in milk, lemon juice, lemon zest, and vanilla extract until combined.
06 - Gradually add the dry ingredients to the wet mixture, stirring just until incorporated to avoid overmixing.
07 - Gently fold fresh or frozen blueberries into the batter with a spatula.
08 - Pour the batter into the prepared loaf pan, smoothing the surface. Evenly sprinkle the cinnamon streusel topping over the batter.
09 - Bake for 50 to 60 minutes, or until a toothpick inserted in the center comes out clean with a few moist crumbs.
10 - Allow the loaf to cool in the pan for 10 minutes. Then remove and transfer to a wire rack to cool completely before slicing.