In a medium bowl combine the all-purpose flour, baking powder, baking soda, salt, and poppy seeds. Whisk together to combine and set aside.
In a large bowl combine the granulated sugar and the lemon zest. Use your fingers to rub the lemon zest into the sugar to release the lemon oils and bring the best flavor.
Add in the melted butter, eggs, sour cream, lemon juice, and vanilla. Whisk it together until well combined.
Tip in your dry ingredients, and fold them together with a rubber spatula alternating with the milk. Take care not to overmix the batter.
Cover the muffin batter bowl and let it sit at room temperature for 30 minutes while you preheat the oven.
Line a muffin pan with 12 paper liners. Divide the batter evenly over the muffin liners.
Bake the muffins at 425°F/220°C for 5 minutes then turn the oven down to 350°F/180°C and continue baking for another 15 minutes or until the tops of the muffins are lightly golden brown and the muffin tops spring back when pressed in the center. For mini muffins, the baking time will need to be reduced.
When the muffins have only a couple of minutes left of baking, mix together the lemon juice and sugar for the topping.
As the hot muffins come from the oven, prick the tops of each muffin a few times with a skewer so the topping can soak in. Then generously drizzle the muffins with the crunchy lemon sugar topping.
Once drizzled, remove the muffins from the tin and let the cool further on a wire rack.
Notes
Both US customary and metric conversions are provided, though I recommend using metric. Use the toggle on the recipe card to switch between the two.