Zest two lemons using a microplane, aiming for about 1 tablespoon zest, and set aside. Squeeze the lemons to extract 1/4 cup fresh lemon juice.
Lightly toast the poppy seeds in a dry skillet over medium heat until fragrant and slightly darker, then transfer to a small bowl to cool.
In a large mixing bowl, whisk together the sifted all-purpose flour, whole wheat flour (if using), sugar, baking powder, salt, and toasted poppy seeds until evenly combined.
In a separate bowl, whisk the eggs, melted butter, lemon zest, lemon juice, and buttermilk until smooth and slightly frothy.
Pour the wet mixture into the dry ingredients, then gently fold with a spatula until just combined. Be careful not to overmix; the batter should be slightly lumpy.
Divide the batter evenly among the muffin cups, filling each about two-thirds full. Gently tap the tin on the counter to settle the batter and eliminate air bubbles.
Bake in a preheated oven at 180°C (350°F) for 18-22 minutes, until the muffins are golden around the edges and a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for about 5 minutes. Then transfer to a wire rack to cool completely or enjoy warm.
Once cooled slightly, serve these bright muffins plain or dusted with powdered sugar, enjoying their fragrant lemon aroma and tender, crumbly texture.
