Prep the pan and oven. Heat your oven to 400°F (200°C).
Line a 12-cup muffin pan with liners or lightly grease it.
Mix dry ingredients. In a large bowl, whisk together flour, sugar, poppy seeds, baking powder, baking soda, and salt until evenly combined.
Whisk wet ingredients. In another bowl, whisk eggs, milk, yogurt (or sour cream), melted butter (or oil), lemon zest, lemon juice, and vanilla until smooth.
Combine gently. Pour the wet mixture into the dry. Stir with a spatula just until no dry streaks remain. The batter should be thick and slightly lumpy—don’t overmix.
Portion the batter. Divide evenly among the muffin cups, filling each about 3/4 full.
For bakery-style domes, let the filled pan sit for 5 minutes before baking.
Bake hot, then lower. Bake at 400°F (200°C) for 5 minutes, then reduce the oven to 350°F (175°C) without opening the door. Bake another 10–13 minutes, until the tops are set and a toothpick comes out clean or with a few moist crumbs.
Cool and glaze. Let muffins cool in the pan for 5 minutes, then move to a rack. If using the glaze, whisk powdered sugar with lemon juice to a pourable consistency and drizzle over warm muffins.
Add zest if you like it extra bold.