01 - Preheat the oven to 350°F. Grease and flour a 9x5-inch loaf pan or line with parchment paper.
02 - Combine flour, granulated sugar, brown sugar, cinnamon, and salt in a small bowl. Cut in cold butter using a fork or fingers until crumbly. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - In a large bowl, beat softened butter and granulated sugar until light and fluffy. Incorporate eggs one at a time, beating thoroughly after each.
05 - Stir in milk, lemon juice, lemon zest, and vanilla extract until fully combined.
06 - Gently fold dry ingredients into wet ingredients until just incorporated; avoid overmixing.
07 - If using frozen blueberries, toss them with 1 teaspoon flour. Fold blueberries into the batter carefully.
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.
10 - Allow the bread to cool in the pan for 15 minutes, then transfer to a wire rack until completely cooled before slicing.