01 - Heat oven to 350°F. Grease and flour a 9x5-inch loaf pan or line it with parchment paper.
02 - Combine flour, granulated sugar, brown sugar, cinnamon, and salt in a small bowl. Cut in cold butter until the mixture is crumbly. Chill until ready to use.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - Using an electric mixer or whisk, beat butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition.
05 - Stir in milk, lemon juice, lemon zest, and vanilla extract until thoroughly combined.
06 - Gently fold dry ingredients into wet ingredients until just combined, avoiding overmixing.
07 - If using frozen blueberries, toss them with 1 tsp flour to prevent sinking. Fold blueberries into the batter.
08 - Pour the batter into the prepared loaf pan and smooth the surface evenly.
09 - Evenly sprinkle the chilled streusel mixture over the batter.
10 - Bake for 50 to 55 minutes, or until a toothpick inserted into the center comes out clean.
11 - Let cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.