Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together the flour, baking powder, and salt until combined.
In a separate bowl or large measuring cup, beat the egg for about 20 seconds, then add the sugar and whisk until well combined.
Slowly whisk in the melted, slightly cooled butter, then add the sour cream and whisk until the wet mixture is smooth.
Toss the blueberries with the dry ingredients to coat them; this helps keep them from sinking.
Pour the sour cream mixture into the bowl with the dry ingredients and gently fold with a spatula until just combined; do not overmix.
Divide the batter among the prepared muffin cups, filling each about 3/4 full.
Bake until the tops are golden and a toothpick inserted into the center of a muffin comes out clean, about 25 minutes.
Let the muffins cool in the pan for about 5 minutes, then transfer to a wire rack to cool slightly before serving.