01 - Preheat oven to 375°F. Line two baking sheets with parchment paper.
02 - In a small bowl, combine flour, brown sugar, cinnamon, and salt. Add cold butter and use a fork or fingers to rub butter into dry ingredients until crumbly. Refrigerate until ready to use.
03 - In a large bowl, whisk together flour, baking powder, baking soda, salt, sugar, and lemon zest.
04 - In another bowl, whisk melted butter, eggs, Greek yogurt, milk, lemon juice, and vanilla until smooth.
05 - Add wet ingredients to dry ingredients and mix gently until just combined, being careful not to overmix.
06 - Fold in blueberries carefully to avoid breaking them and prevent overmixing.
07 - Using a large cookie scoop or 1/4 cup measure, drop mounds of batter onto prepared baking sheets, spacing at least 2 inches apart with approximately 6 mounds per sheet.
08 - Sprinkle each muffin top generously with prepared streusel mixture.
09 - Bake for 13 to 16 minutes, or until edges are golden brown and a toothpick inserted in the center comes out clean.
10 - Cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.