01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly with butter.
02 - In a small bowl, combine flour, sugar, cinnamon, and salt. Cut in the cold butter using your fingertips or a pastry cutter until mixture resembles coarse crumbs. Set aside.
03 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and lemon zest until well combined.
04 - In a separate bowl, whisk eggs, milk, oil, yogurt (or sour cream), lemon juice, and vanilla extract until smooth and uniform.
05 - Pour the wet mixture into the dry ingredients. Gently fold together using a spatula until just combined. Do not overmix—small lumps are acceptable.
06 - Gently fold in the fresh or frozen blueberries until evenly distributed throughout the batter.
07 - Divide the batter evenly among the 12 muffin cups. Sprinkle each muffin generously with the prepared streusel topping.
08 - Bake for 20 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
09 - Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.