Preheat oven to 350. Coat a 9x5" loaf pan with cooking spray. Cut a strip of parchment paper long enough to cover bottom and two ends, for easy removal. Coat parchment with cooking spray. Set aside.
In a large bowl whisk together flour (use a spoon to fill measuring cup - scooping directly into flour will result in too much flour), surgar, baking soda and salt. Set aside.
In a medium bowl whisk together buttermilk, egg, butter and vanilla.
Pour buttermilk mixture into dry ingredients. Stir until just combined and smooth. Fold in blueberries.
Pour batter into prepared pan and bake for 55-65 minutes. Use a toothpick inserted into center to test doneness.
Allow bread to cool for 15-20 minutes in the pan and then transfer bread to a wire rack to cool completely.
Glaze bread when it's cooled. Whisk together powdered sugar, vanilla, milk and lemon juice until smooth. Drizzle over bread.
Serve warm or at room temperature. Store at room temp for up to 3 days or in refrigerator, for longer.
Notes
If you don't have buttermilk, simply stir 1 tbsp lemon juice or distilled white vinegar into milk to equal 1 c. To achieve the consistency of buttermilk, use whole milk or cream.