Heat the oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners or lightly grease the wells.
Whisk flour, sugar, baking powder, and salt in a large bowl. In a second bowl, whisk the egg, milk, oil, and vanilla until combined.
Pour the wet mixture into the dry ingredients. Fold with a spatula just until no dry pockets remain; a few small lumps are fine.
Fold in the blueberries gently. If using frozen berries, add them straight from the freezer and avoid overmixing to limit streaking.
Divide batter among the muffin cups, filling each about three-quarters full. Sprinkle with coarse sugar if desired.
Bake for 18 to 22 minutes, until the tops spring back lightly and a toothpick inserted in the center comes out without wet batter. Cool in the pan for 5 minutes, then move to a rack.