Preheat oven to 350°F and line a 9"x 5" loaf pan with parchment paper (or lightly grease with butter).
In a medium bowl, whisk the flour, baking powder and salt, and set aside.
In the bowl of an electric mixer, blend together the melted butter, sugar, eggs, vanilla, lemon zest and lemon juice. Mix until well combined.
While slowly mixing, add flour mixture and milk in two batches. Stop mixing as soon as it's just combined.
Rinse off the blueberries (if using fresh) and toss them in a small bowl with 1 tablespoon of flour.
Add the flour coated berries to the batter and gently stir by hand to combine.
Pour batter into prepared pan and bake for 55-65 minutes, or until a toothpick inserted in the center comes out clean. Cool for about 30 minutes.
Prepare glaze by whisking together melted butter, powdered sugar, lemon juice and vanilla, then pour over the loaf. Allow to set a few minutes, then enjoy!