Zest Infusion: In a large mixing bowl, combine the granulated sugar and fresh lemon zest. Use your fingertips to rub them together until the sugar is fragrant and moist.
Dry Whisk: Whisk the all-purpose flour, poppy seeds, baking powder, baking soda, and fine sea salt directly into the lemon sugar mixture.
Wet Emulsion: In a separate bowl, whisk together the melted unsalted butter, sour cream, fresh lemon juice (about 60ml), eggs, and pure vanilla extract until completely smooth.
Combine Batter: Pour the wet ingredients into the dry mixture. Use a silicone spatula to fold the ingredients together gently until just combined—do not over-mix; a few small lumps are perfectly fine.
Tin Distribution: Divide the batter evenly among 12 paper-lined muffin cups, filling each nearly to the top to encourage a tall dome.
Bake: Bake in a preheated oven at 375°F (190°C) for 18 to 20 minutes, or until the tops bounce back lightly when pressed and a toothpick inserted into the center comes out clean.
Cool: Allow the muffins to sit in the hot pan for 5 minutes before transferring them to a wire rack to cool completely before glazing or serving.