Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment paper, leaving an overhang to lift the loaf out easily.

In a medium bowl whisk together flour, baking powder, baking soda, and salt. Set aside.

In a large bowl, rub the lemon zest into the sugar with your fingertips to release oils. Add eggs, melted butter, sour cream, milk, vanilla, and lemon juice; whisk until smooth.

Fold the dry ingredients into the wet just until combined. Be careful not to overmix — a few streaks of flour are fine.

If using frozen blueberries, toss them with 1 tablespoon flour. Gently fold blueberries into the batter so they’re evenly distributed.

Spoon batter into prepared pan and smooth the top. Bake 50–60 minutes or until a toothpick inserted near the center comes out with a few moist crumbs. Tent with foil if top is browning too quickly.

Cool the loaf in the pan for 10 minutes, then lift out and finish cooling on a wire rack. Whisk powdered sugar with lemon juice to desired consistency and drizzle over the cooled loaf.