Turn on your waffle iron to heat it.
In a large bowl, mix the dry ingredients (flour, sugar, poppy seeds, baking powder, baking soda, salt, and orange zest).
1¾ cup (225 grams) bleached all purpose flour, ¼ cup granulated sugar, ¼ cup poppy seeds, 2 teaspoons baking powder, ¼ teaspoon baking soda, ½ teaspoon salt
In a large measuring cup, add the orange juice and then add milk so that the liquid total is 1 cup. Add the eggs and Grand Marnier and beat lightly until uniform.
zest and juice from two small or one medium orange, separated, up to 1 cup milk, to total 1 cup of liquid, 2 eggs, see note about separating if desired, 1 teaspoon Grand Marnier or other orange liqueur
Add the liquid from the measuring cup and the melted butter to the dry ingredients. Mix together only until the mixture has been incorporated fully. Do not overmix.
5 tablespoons (71 grams) unsalted butter, melted
Preheat your waffle iron and waffle per the manufacturer's instructions.