Preheat oven to 400 degrees. Grease a muffin tin or line it with paper or silicone baking cups.
Combine flour, sugar, baking powder, and salt in a large bowl using a whisk.
Combine eggs, milk, butter, and vanilla in another bowl using a whisk.
Stir the wet ingredients into the dry ingredients; then fold in blueberries and sour cream with a spatula. Fill muffin cups ⅔ of the way with batter. Sprinkle tops with sugar. Bake for 15 minutes.