In a large bowl, whisk together the flour, sugar, baking powder, salt, and poppy seeds.
In a medium bowl, beat together eggs, milk, lemon zest, and butter.
Add the egg mixture to the dry ingredients and whisk by hand or use a hand mixer to combine just until no lumps remain. This batter can be refrigerated for up to two days.
Preheat a waffle iron according to manufacturer's instructions. Grease the heated iron with butter. Pour in a ladleful of the prepared batter, about 1/4 cup. Heat until the waffle is cooked through and starting to turn golden. Transfer to a plate and repeat with remaining batter.