Heat the oven to 350°F (175°C). Grease a 9 x 5-inch loaf pan and line it with parchment, leaving enough parchment over the long sides to lift out the baked bread.

Whisk the flour, baking powder, and salt together in a medium bowl. Scoop out 1 tablespoon of this flour mixture and toss it with the blueberries immediately before folding them into the batter.

Beat the softened butter and granulated sugar for 2–3 minutes, until the mixture looks light and fluffy. This helps create a fine, tender texture in the finished loaf.

Beat in the eggs one at a time, mixing after each addition. Add the vanilla, finely grated lemon zest, and 1–2 tablespoons of fresh lemon juice.

Add the dry ingredients in two or three additions, alternating with the milk. Mix only until the ingredients are combined, since overmixing can make the bread dense.

Gently fold the flour-coated blueberries into the batter. Use a light touch so the berries stay intact and the batter does not become heavily streaked.

Spread the batter evenly in the prepared loaf pan. Bake for 55–65 minutes, checking near the 55-minute mark, until a toothpick inserted in the center comes out clean or with a few moist crumbs.

Cool the loaf in the pan for 10–15 minutes, then use the parchment to transfer it to a wire rack. Let it cool completely, for at least 30 minutes, before adding the glaze.

Whisk the confectioners' sugar with 2 tablespoons of lemon juice and the optional lemon zest. Drizzle the glaze over the completely cooled loaf, then allow it to set briefly before slicing.