Preheat oven to 400°F (200°C) and line a 12-cup muffin tin. Whisk the flour, sugar, baking powder, and salt for 30 seconds.

In a separate bowl, whisk the egg, milk, melted butter, sour cream, and vanilla until smooth, about 1 minute.

Pour the wet mixture into the dry and stir with a spatula just until no dry flour remains, about 15 to 20 strokes.

Gently fold in the blueberries with two or three turns of the spatula.

Divide batter evenly among the muffin cups and bake for 18 to 22 minutes, until golden and a toothpick comes out with a few moist crumbs. Cool in the pan for 5 minutes, then transfer to a wire rack.