1) Make the batter: Preheat oven to 400 degrees F.  Lightly coat a 12-cup muffin tin with vegetable-oil cooking spray.  Set aside.  In a large bowl, combine 2-1/4 cups flour, sugar, baking powder, and salt and set aside.  In a medium bowl, whick together eggs, sour cream, butter, cup milk, lemon juice and zest.  Using a fork, stir the egg mixture into the flour mixture until just combined.  Do not overmix.  In a small bowl, combine remaining 3 tablespoons flour and blueberries, toss to coat, and gently fold into batter.
2)  Bake the muffins:  Spoon 1/3 cup of batter into prepared muffin cups.  Sprinkle sugar evenly over each filled muffin cup, if desired.  Bake the muffins until the tops are golden - 30 to 35 minutes.  Cool 5 minutes on a wire rack.  Loosen edges and turn the muffins out onto the rack to cool completely.  Store in an airtight container for up to 4 days.