01 - Preheat oven to 350°F. Grease and flour a 9x5-inch loaf pan or line it with parchment paper.
02 - Combine flour, sugars, cinnamon, and salt in a small bowl. Cut in cold butter until crumbly. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - Beat butter and granulated sugar with an electric mixer until light and fluffy. Add eggs one at a time, beating well after each.
05 - Stir in milk, lemon juice, lemon zest, and vanilla extract until combined.
06 - Gently fold dry ingredients into wet without overmixing, stopping when just combined.
07 - If using frozen blueberries, toss them with 1 tsp flour. Fold berries carefully into the batter.
08 - Pour batter into prepared loaf pan and smooth surface evenly.
09 - Sprinkle chilled streusel mixture evenly over the batter.
10 - Bake for 50 to 55 minutes, or until a toothpick inserted in the center comes out clean.
11 - Let bread cool in pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.