01 - Set oven temperature to 375°F. Line two standard baking sheets with parchment paper.
02 - In a small mixing bowl, combine flour, brown sugar, cinnamon, and salt. Add cold cubed butter and use a fork or fingertips to rub mixture until it resembles coarse breadcrumbs. Refrigerate until needed.
03 - In a large mixing bowl, whisk together flour, baking powder, baking soda, salt, sugar, and lemon zest until evenly distributed.
04 - In a separate bowl, whisk melted butter, eggs, Greek yogurt, milk, lemon juice, and vanilla extract until smooth and fully combined.
05 - Pour wet ingredients into dry ingredients and fold gently with a spatula until just combined. Do not overmix, as this will affect texture.
06 - Gently fold blueberries into batter, taking care to minimize stirring to prevent bruising and color bleeding.
07 - Using a large cookie scoop or 1/4 cup measure, drop batter mounds onto prepared baking sheets, spacing approximately 2 inches apart, placing about 6 mounds per sheet.
08 - Distribute streusel topping generously over each muffin mound.
09 - Place in preheated oven and bake for 13 to 16 minutes, or until edges are golden brown and a toothpick inserted into the center emerges clean.
10 - Allow muffins to rest on baking sheets for 5 minutes, then transfer to a wire cooling rack until completely cooled.