Preheat the Oven: Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or lightly grease the pan.
Combine Dry Ingredients: In a large bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon.
Mix Wet Ingredients: In a separate bowl, whisk the melted butter, milk, eggs, and vanilla extract until well combined.
Fold in Wet and Dry Ingredients: Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix.
Add Blueberries: Gently fold in the blueberries (and lemon zest if using) with a spatula, ensuring they are evenly distributed without crushing them.
Scoop and Fill: Using a large spoon or ice cream scoop, portion the batter into the muffin tin, filling each cavity about 2/3 full.
Sprinkle Sugar (Optional): Sprinkle coarse sugar on top of each muffin top for a crunchy finish.
Bake: Bake in the preheated oven for 18–20 minutes or until a toothpick inserted into the center comes out clean, and the muffin tops are golden brown.
Cool and Serve: Allow the muffin tops to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. Enjoy!