Preheat the oven to 425°F. Line a 12-cup muffin pan with cupcake liners or spray with non-stick cooking spray.
Sift together flour, salt, and baking powder in a small bowl and set aside.
In a large mixing bowl beat or whisk together eggs, melted butter, sugar, vanilla extract, buttermilk, and sour cream.
Dump dry ingredients into the butter/eggs/sour cream mixture and stir gently, just until combined. Do not overmix.
Toss 1 cup of blueberries with 1 remaining tablespoon of flour and fold into the muffin batter.
Divide batter between the 12 muffin cups in the prepared pan, filling each cup about ¾ of the way full.
Sprinkle brown sugar over the top of the muffins.
Bake for 6 to 7 minutes at 425°F and then turn the oven down to 375°F and continue baking an additional 10 to 12 minutes until a toothpick inserted in the center of the muffins comes out clean and the tops are golden brown.
Cool muffins in pan for 5 minutes. Remove muffins to a cooling rack to finish cooling.