Separate egg whites and yolks in two bowls, and set aside. Warm milk and combine with yeast and sugar. Allow to bloom for 10 min.
Lightly beat yolks and add warmed milk and yeast. Beat until incorporated, then add sparkling water and stir gently until well-combined. Sift flour directly into the milk mixture, beat with an electric mixer until all lumps are smoothed out.
Melt butter in a small sauce pan and beat egg whites into stiff peaks. Pour melted butter into batter and gently fold in stiffened egg whites by hand, and add a pinch of salt as well. Set batter aside for 20-30 minutes, so yeast can work and batter has time to rise.
When the batter shows bubbles an appears “alive”, you’re ready to start baking!
Make sure to butter all sides of your waffle iron, regardless of whether it is non-sticker not. Pour 1/3 cup of batter per waffle, and allow waffle to brown completely. Every waffle iron is different, so it’s a bit hard for me to say how long this will take with your machine. You want the waffles to be crisp and brown on the outside.
Serve with powdered sugar, brown sugar or whipped cream for an authentic Belgian treat… or go a bit crazy and add crisped bacon, ham or cheese to the batter for a hearty salty & sweet combination!