Light as air, this batter is quite forgiving and will stand for at least an hour before using. Brunch is often enjoyed with wine and the sweet and savoury flavours here perfectly match the fruity richness of gewurztraminer.
Whisk the egg yolks, butter, buttermilk and soda water until smooth. Fold in the egg whites. Gradually fold into the dry ingredients until well combined.
Lightly brush a heated waffle iron with oil.
Add 1 heaped tablespoon of the batter onto each iron spreading it evenly and into the corners. Top with a tablespoon each of ham and grated cheese. Close the iron and cook, until golden.
Remove to an oven tray and keep warm in a 150C oven while preparing the remainder.