01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly with butter or cooking spray.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Add cold cubed butter and blend with fingers or pastry cutter until mixture resembles coarse crumbs. Set aside in refrigerator.
03 - In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, salt, and lemon zest until well incorporated.
04 - In a separate bowl, whisk eggs, milk, vegetable oil, Greek yogurt, lemon juice, and vanilla extract until smooth and emulsified.
05 - Pour wet ingredients into dry ingredients. Stir gently with a spatula or wooden spoon until just combined. The batter will remain slightly lumpy. Do not overmix.
06 - Gently fold blueberries into the batter using a light folding motion. If using frozen berries, add directly from freezer without thawing.
07 - Divide batter evenly among the 12 muffin cups, filling each about three-quarters full.
08 - Sprinkle prepared streusel topping generously over the surface of each muffin, pressing lightly to adhere.
09 - Bake at 375°F for 20 to 22 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs attached.
10 - Allow muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.