Preheat your oven to 400 degrees F. Line a 12-cup muffin tin with paper liners; set it aside.

In a large bowl, sift together 3 cups of the flour, baking powder, and salt; set aside.

In another large bowl, use a handheld electric mixer or a stand mixer fitted with a paddle attachment to combine the butter, sugar, lemon zest, and vanilla extract. Beat on medium speed until light and fluffy, about 3 minutes.

Add the eggs, one at a time, beating well after each addition. Remember to scrape down the sides of the bowl as needed.

In a separate bowl or measuring cup, whisk together the sour cream and lemon juice; set aside.

In another bowl, toss the blueberries with the remaining flour to coat.

With the mixer on low, alternate adding the flour mixture and the sour cream mixture, starting and ending with the flour. Be careful not to overmix.

Gently fold in the blueberries and poppy seeds just until combined.

Divide the batter evenly among the prepared muffin tins.

Bake for 25 to 27 minutes, until the muffins are lightly golden and a toothpick comes out clean.

Let the muffins cool in the pan for 10 minutes before transferring them to a cooling rack.

In a medium bowl, whisk together the confectioners' sugar, lemon juice, zest, and milk until smooth. Drizzle this over the muffins before serving.