Heat oven to 350°F. Grease a 8.5x4.5-inch loaf pan and line with a parchment sling.
Rub lemon zest into the sugar with your fingertips until fragrant and slightly moist.
Whisk flour, baking powder, baking soda, and salt in a medium bowl.
Whisk melted butter with the lemon sugar until glossy. Beat in the beaten eggs until smooth.
Add yogurt, lemon juice, and vanilla. Whisk in buttermilk until combined.
Stir dry ingredients into wet just until no dry pockets remain. Do not overmix.
Toss blueberries with 1 tbsp flour, then gently fold them into the batter.
Spread batter into the pan and smooth the top. Tap the pan once to release bubbles.
Bake 50–60 minutes, until a tester in the center comes out clean. Tent with foil if browning early.
Cool 15 minutes in the pan, then lift out and cool completely.
Whisk powdered sugar, lemon juice, and milk to a thick drizzle. Pour over the cooled loaf and let set before slicing.