Preheat the oven to 350 degrees F. Grease a standard 12-cup muffin tin (or line with paper liners) and set aside.
Whisk the flour, baking powder and salt in a large bowl untill combined.
Whisk the egg in a separate medium bowl until well-combined and light-colored, about 20 seconds. Add the sugar and whisk vigorously until thick, about 30 seconds. Add the melted butter in 2 additions, whisking gently to combine after each addition. Add the sour cream in 2 additions, whisking just to combine.
Add the blueberries to the dry ingredients and gently toss just to combine. Add the sour cream mixture and fold with a rubber spatula until the batter comes together and the blueberries are evenly distributed, 25 to 30 seconds. Small spots of flour may remain and the batter will be very thick. Do not overmix.
Divide the batter among the muffin cups (a large cookie scoop works great for this!). Bake until the muffins are light golden brown and a toothpick or thin knife inserted into the center of a muffin comes out clean, 25 to 30 minutes. Immediately remove muffins to a wire rack and cool for at least 5 minutes. Serve immediately or at room temperature. Store leftovers in an airtight container at room temperature for up to 4 days or in the refrigerator for up to 1 week.