In a medium bowl, whisk the dry ingredients together: flour, cornmeal, baking powder, salt and sugar.
To a measuring cup or small bowl, measure out the milk. And then whisk in the egg yolks and melted butter. Add the wet ingredients into the dry and mix just until combined (some lumps are totally fine).
Pour the egg whites into a separate bowl and using an electric-hand mixer or a stand-up mixer with the whisk attachment, beat until stiff peaks form, about 3 to 4 minutes. Fold the egg whites into the batter until combined.
Place the ebelskiver pan over medium heat. Warm for about 2 to 3 minutes. Turn the heat to medium-low. Brush the cavities of the ebelskiver pan liberally with butter. This will do two things: give the ebelskivers some nice flavor and ensure that nothing sticks. Fill the cavities with about 2 tablespoons of batter. Allow to cook until small bubbles form on the surface, about 2 minutes. Using an offset spatula, turn the ebelskiver 90 degrees and then add another scant tablespoon of batter. (This will give you a perfect round-shape of an ebelskiver, if you don’t care about perfection, skip this step and flip it over and cook on the opposite side for another 2 minutes.) Cook for 1 to 2 minutes and then flip again and cook for an additional 1 to 2 minutes.