Preheat the oven to 400F.
Grease a 12-muffin tin or line with paper liners.
Mix the dry ingredients together in a bowl (flour, baking powder, baking soda, salt and nutmeg).
Mix the eggs, sour cream, sugar, melted butter and vanilla in a small bowl.
Stir the wet and dry ingredients together except for the blueberries. Don't overmix. The batter shouldn't be totally smooth but should be well blended. Then fold in (stir gently) the blueberries.
Divide the batter among the 12 muffin tins. Top with cinnamon sugar.
Bake 20-25 minutes. Test with a toothpick or knife by inserting into the middle of a muffin. It should come out clean when they are done.
Let cool on a wire rack 5 minutes before removing from pan, the continue to cool the muffins on a wire rack.