Preheat the oven to 425°F (220°C). Line two 12-count muffin pans with paper liners or grease the pan.
In a large bowl, whisk together the flour, poppy seeds, baking powder, baking soda, and salt.
2 cups all-purpose flour, 1 tablespoon poppy seeds, 1 teaspoon baking powder, ½ teaspoon salt, ½ teaspoon baking soda
In another bowl, beat the sugar and butter until lightened in color and creamy.
½ cup unsalted butter, ¾ cup granulated sugar
Add the eggs, sour cream, milk, lemon juice, lemon zest, and vanilla. Mix until well combined.
2 large eggs, ½ cup sour cream, ½ cup whole milk, ¼ cup fresh lemon juice, 1 tablespoon lemon zest, 1 teaspoon vanilla extract
Add the dry ingredients to the wet and mix until no streaks of flour remain. The batter will have a thick, fluffy texture.
Divide the batter evenly between the muffin cups, filling each about ¾ full.
Bake for 5 minutes at 425°F (220°C), then lower the oven to 350°F (175°C) and bake for an additional 15 to 17 minutes. A toothpick inserted in the center should come out clean when the muffins are done.
Cool the muffins in the pan for 5 minutes, then transfer to a wire rack.