In a small bowl, whisk together flour, baking powder, salt, and poppy seeds. Set aside.
In another bowl rub the white sugar and lemon zest together until it resembles wet sand and smells aromatic. Add the softened butter to the lemon sugar mixture and cream together for 2-3 minutes until light and fluffy.
Add the eggs and vanilla extract and beat until smooth.Add the buttermilk and lemon juice.
Pour the dry ingredients into the wet ingredients and gently fold until just combined. Do not overmix.
Toss the blueberries with 1 tablespoon of flour, then gently fold them into the batter.
Let the muffin batter rest at room temperature for 30 minutes.
Preheat the oven to 425 degrees and line a 12 count muffin pan with paper liners. (Option: For taller muffins, only fill every other muffin cup (six total).)
Once the batter has rested, do not stir. Gently scoop the batter into the prepared cups, filling them all the way to the top.Overfill the batter into the muffin liners.
Bake the muffins for 5 minutes at 425 F. Reduce the oven temperature to 375 for the remaining time, about 17-20 minutes.until a toothpick inserted into the center of the muffin comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely.
While muffins cool, whisk together the powdered sugar and lemon juice for the glaze. Drizzle over cooled muffins.