Preheat Oven: Set oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or lightly grease.
Mix Dry Ingredients: In a large bowl, whisk together flour, sugar, salt, and baking powder.
Mix Wet Ingredients: In a measuring cup, whisk oil (or melted butter), egg, vanilla, and enough milk to make 1 cup total liquid.
Combine: Pour wet ingredients into the dry and stir gently until just combined (batter will be lumpy—don’t overmix).
Add Blueberries: Fold in blueberries carefully so they don’t burst too much.
Fill Muffin Cups: Divide batter evenly among the 12 cups, filling about ¾ full. Sprinkle tops with coarse sugar if using.
Bake: Bake 18–22 minutes, or until golden and a toothpick inserted in the center comes out clean.
Cool & Enjoy: Let muffins cool a few minutes before removing from the tin. Best eaten warm with a pat of butter.