Preheat the oven to 400℉. Line a 12-cup muffin tin (or a 6-cup muffin tin) with paper liners (or just spray with nonstick spray).
MAKE THE MUFFINS:
In a large bowl, whisk together the flour, poppy seeds, baking powder and salt.
In a separate bowl, whisk together the milk, eggs, sugar, butter, lemon zest and lemon extract.
Add the milk mixture to the flour mixture and stir together until just combined. Divide the batter between the muffin cups.
Bake for about 17 minutes (for regular-sized muffins), until a toothpick inserted into a muffin comes out clean. Jumbo muffins will bake for 23 to 24 minutes. Transfer to a wire rack to cool.
ADD GLAZE:
In a medium bowl, whisk the powdered sugar with 2 tablespoons of lemon juice. Whisk in more lemon juice, as needed. Drizzle over muffins.