For topping, mix togather sugar and lemon zest, set aside.
oven to 425 degrees.Bring 1 cup blueberries and 1 teaspoon sugar to a simmer in saucepan over medium heat.mashing berries with spoon and stirring frequently, until berries have broken down and mixture is thicken and reduced.set aside in a bowl and let cool.
In a mixing bowl combine dry ingredients togather, in a separate bowl whisk 1 cup of sugar and eggs together ,until combined. stir in buttermilk and vanilla until combined. gently fold in egg mixture and remaining cup of blueberries into flour mixture until moistened.
Please dont over mix. I use a ice cream scoop to put batter equally among prepared muffin cups. spoon teaspoon of cooked berry mixture into center of each mound of batter. gently swirl berry filling into the batter.
Sprinkle lemon sugar evenly over muffins. Bake until muffin tops are goldern and firm 20 minutes.Cool muffins for 5 minutes then tranfer to wire rack.