Preheat the oven: Set your oven to 375°F (190°C). Line a muffin tin with paper liners or lightly grease it.
Mix the dry ingredients: In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
Beat wet ingredients: In a large bowl, whisk together the melted butter and sugar until smooth. Add the eggs and vanilla extract, then mix until combined.
Add the milk: Pour in the milk and stir until the mixture is smooth and creamy.
Combine dry and wet ingredients: Gradually add the dry ingredients to the wet mixture. Stir until just combined—don’t overmix.
Prepare the blueberries: Toss the blueberries with 1 tablespoon of flour to keep them from sinking in the batter.
Fold in the blueberries: Gently stir the blueberries into the batter, being careful not to mash them.
Fill the muffin cups: Spoon the batter into the prepared muffin tin, filling each cup about 3/4 full.
Add sugar topping: If using, sprinkle a little coarse sugar on top of each muffin for that classic muffin-top crunch.
Bake the muffins: Place the muffin tin in the oven and bake for 18–20 minutes, or until a toothpick inserted into the center comes out clean.
Cool and enjoy: Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to finish cooling—or eat warm for maximum deliciousness.