Preheat the oven to 350°F. Butter and flour the bottom and sides of a 9 x 5-inch loaf pan, tapping out any excess flour.
In a large bowl, combine the flour, sugar, baking powder, and salt. Whisk until well-combined.
In a medium sized mixing bowl, whisk together the milk, eggs, and vanilla beans.
Pour the wet ingredients over the dry ingredients and add the melted butter. Gently fold with a silicone spatula until all of the ingredients are incorporated.
Scrape half of the batter into the prepared pan and top with 3 tablespoons of the blueberry syrup. One tablespoon at the far end of the pan, one in the middle, and one on the other side. Use a wooden skewer or a toothpick to swirl the blueberry syrup into the batter. Add the second half of the batter to the pan and gently smooth the top with a spatula. Add the 3 remaining tablespoons of blueberry syrup as described above and swirl with a wooden skewer.
Bake, rotating the pan halfway through the cooking time, until the top is golden brown and a toothpick inserted in the center comes out clean, 50-55 minutes.
Leave the bread in the pan and allow it to cool completely on a wire rack before glazing.
To glaze the bread:
Whisk the confectioners' sugar and the blueberry syrup in a small bowl until completely combined and no lumps remain. If the mixture seems too thick you can add an additional teaspoon at a time of syrup to thin it out; you don't want it to be too thin or it will all run off of the bread!
Carefully remove the bread from the pan and place it back onto the cooling rack. Put paper towels or a plate underneath the rack to catch the drips. Pour the glaze evenly across the top of the bread and allow it to drizzle down the sides. Leave the bread undisturbed for 15-20 minutes for the glaze to set
