Prep the Oven and Pan: Start by heating the oven to 375°F. Line a muffin tin with paper liners or lightly grease each cup. This helps the muffins release easily and keeps the edges soft. Set the pan aside so it stays ready once the batter comes together.
Mix the Dry Ingredients: Grab a large bowl and add flour, baking powder, salt, sugar, and poppy seeds. Stir everything gently so the baking powder spreads evenly. This step helps the muffins rise evenly and keeps the texture light.
Combine the Wet Ingredients: In another bowl, whisk the melted butter with eggs until smooth. Add milk, sour cream, vanilla extract, lemon juice, and lemon zest. Whisk until the mixture looks creamy and well blended. The lemon scent should already feel bright at this stage.
Bring the Batter Together: Pour the wet mixture into the dry ingredients slowly. Stir just until the flour disappears. The batter should look thick yet smooth. Overmixing can make muffins dense, so stop once everything looks combined.
Fill the Muffin Cups: Spoon the batter evenly into the prepared muffin tin. Fill each cup about three quarters full to allow room for rising. Gently tap the pan on the counter to release air bubbles.
Bake Until Lightly Golden: Slide the pan into the oven and bake for 18 to 22 minutes. The tops should look lightly golden and spring back when touched. A toothpick inserted into the center should come out clean.
Make the Lemon Glaze: While the muffins cool slightly, mix icing sugar with lemon juice until smooth. Drizzle the glaze over warm muffins so it sets softly and adds extra citrus flavor.
