Adjust the oven rack to the 2nd level mark, just above center, and preheat the oven to 400ºF. Line a standard size muffin tin with tulip liners. If you're using standard size liners you will yield more muffins. If not using any liners, generously spray the muffin tin cavities well with a flour-based baking spray.
In a medium-size mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
In a separate medium-size mixing bowl, whisk together the eggs, granulated sugar, melted butter, lemon zest, and lemon juice. Then add in the buttermilk and vanilla extract.
Using a spatula, gradually add the dry ingredients to the wet mixture stirring until just combined. Gently fold in the blueberries. Optional step: coat the blueberries in flour before adding them to the batter. This can prevent blueberries from sinking to the bottom during baking.
Using a 3 tablespoon-size cookie scoop or two spoons, evenly divide the batter into the muffin liners, filling them to the top. Do this only if you are using the tulip liners. If using standard size liners, fill them ⅔ full. Top with any extra blueberries (optional) and streusel.
Bake for 18-20 minutes at 400ºF or until an inserted toothpick comes out clean. When done, remove from the oven and allow to cool for 5 minutes before removing muffins from the tin.
Muffins are best served still warm with a little butter, but are equally just as good completely cooled.