In a medium bowl sift and mix all the dry ingredients together (flour, baking powder, baking soda, salt, granulated sugar and brown sugar).
In another bowl, mix the eggs, buttermilk, melted butter, sour cream and vanilla.
Pour the egg mixture onto the flour mixture and mix only until well integrated.
Place the blueberries in a small bowl and add the extra tsp of flour. Mix carefully using your fingers to coat each blueberry with flour (this will make the blueberries spread evenly throughout the batter while baking, instead of them just staying in one spot). Lastly, add the blueberries carefully to the batter.
Now, pour the batter into cupcake pans (previously lined with cupcake liners) filling about 3/4 each.
Bake the muffins for about 20 min. or until they turn golden brown on the top.