01 - Preheat oven to 400°F. Line a 12-cup muffin tin with paper liners or grease cups thoroughly with cooking spray.
02 - In a large mixing bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt until evenly distributed.
03 - In a separate bowl, whisk eggs, vegetable oil or melted butter, yogurt or buttermilk, lemon zest, lemon juice, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Gently fold together with a spatula just until combined—batter should remain slightly lumpy. Do not overmix.
05 - Toss blueberries with 1 tablespoon flour in a small bowl to prevent sinking, then gently fold into batter.
06 - Divide batter evenly among the 12 muffin cups, filling each about three-quarters full. Sprinkle tops with coarse sugar if using.
07 - Bake for 18–22 minutes until muffins are golden brown and a toothpick inserted into the center comes out clean.
08 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.