01 - Preheat oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners or grease lightly.
02 - Combine flour, brown sugar, cinnamon, and salt in a small bowl. Add cold butter and rub with fingers or fork until coarse crumbs form. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - In a large bowl, whisk melted butter and sugar until smooth. Incorporate eggs one at a time, mixing well after each. Stir in Greek yogurt, milk, lemon zest, lemon juice, and vanilla extract until homogeneous.
05 - Fold dry ingredients into wet mixture gently until just combined, avoiding overmixing.
06 - Fold in blueberries carefully to distribute evenly.
07 - Divide batter evenly into muffin cups, filling each about three-quarters full. Top with streusel evenly.
08 - Bake for 20 to 22 minutes until a toothpick inserted in the center comes out clean.
09 - Allow muffins to cool in pan for 5 minutes, then transfer to wire rack to cool completely.