Prepare the loaf pan. Heat the oven to 350°F (175°C). Grease the pan and add a parchment sling extending over the long sides.
Whisk flour, baking powder, baking soda, and salt. Rub lemon zest into granulated sugar until fragrant, then beat with butter for 3 minutes.
Beat in eggs one at a time. Mix in sour cream, lemon juice, and vanilla, scraping the bowl to combine everything evenly.
Fold the flour mixture into the wet ingredients just until combined. Toss blueberries with their tablespoon of flour and fold gently into the batter.
Scrape into the pan and level the surface. Bake 50–60 minutes; tent loosely with foil if darkening before the middle is cooked.
Check the center with a skewer, avoiding a blueberry. A few moist crumbs are fine, but there should be no raw batter.
Cool in the pan for 15 minutes, then lift onto a rack and cool fully. Whisk powdered sugar with enough lemon juice for a thick drizzle.
Spoon glaze over the cooled loaf. Allow it to settle before slicing, wiping the knife between cuts for a tidy presentation.
