Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease it well.
In a large bowl, whisk together the 2 cups of flour, sugar, baking powder, and salt.
In a separate medium bowl, whisk together the melted butter, egg, milk, and vanilla extract until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix; a few lumps are okay.
In a small bowl, toss the blueberries with the 1 tablespoon of flour. This helps prevent them from sinking to the bottom of the muffins.
Gently fold the floured blueberries into the muffin batter. Be careful not to overmix, as this can turn your batter blue.
Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full.
Bake for 18-22 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
Notes
For extra moist muffins, you can substitute 1/2 cup of the milk with plain yogurt or buttermilk.
If using frozen blueberries, do not thaw them before tossing with flour and folding into the batter.
A hint of lemon zest added to the batter can brighten the blueberry flavor.
For bakery-style muffins, you can add a simple streusel topping before baking. Mix 1/4 cup flour, 2 tablespoons sugar, and 2 tablespoons cold butter until crumbly, then sprinkle over the batter.