Preheat oven to 400°F (204°C) and line mini muffin tin with paper liners. Lightly grease the top of the pan to prevent sticking.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.
In a separate measuring cup, whisk the oil, egg, and vanilla, then add milk until it reaches the 1-cup mark. Stir well.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. Do not overmix.
Fold in the blueberries carefully, ensuring they are evenly distributed. Let the batter rest for 5 minutes.
Scoop batter into mini muffin cups, filling nearly to the top. Sprinkle a little sugar on each muffin for a crunchy top.
Bake for 12-15 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely. Enjoy warm or at room temperature!