Preheat your oven to 425°F. Add liners to every other cup in a muffin pan.
In a large bowl, mix together the dry ingredients: flour, sugar, baking powder, salt, and the optional cinnamon.
In another bowl, whisk together the melted butter, eggs, buttermilk, vanilla extract, and the lemon zest/juice.
Pour the wet ingredients into the dry bowl and gently fold using a wooden spoon. Do not over mix! The batter will be thick and you should still see little pockets of flour.
If using frozen blueberries: Rinse the frozen blueberries with cold water, using a strainer, until the water runs clear. Pat the berries dry with a paper towel, then toss with 1 - 2 tablespoons of flour. If using fresh blueberries: Proceed to Step 6. Gently fold in the blueberries - again, do not over mix.
Fill the cupcake liners to the top, being sure to only fill every other muffin cup in the cupcake tin. Sprinkle the batter with optional turbinado sugar.
Bake at 425℉ for 5 minutes, then turn the oven temperature down to 350℉ and bake for 18-20 minutes. A toothpick stuck in the middle should have a bit of crumb on it.
Remove the muffins from the muffin tin, and let them cool on a wire rack. Enjoy!