Makes 12 waffles
1 3/4 cups all-purpose flour
Preheat oven to 300° Fahrenheit. Heat waffle iron until very hot.
Whisk flour, sugar, baking powder, baking soda, and salt in a large bowl. Using an electric mixer, beat egg whites in a medium bowl until medium-soft peaks form. In a separate, medium bowl, whisk the egg yolks, melted butter, buttermilk, and soda water; gradually whisk into dry ingredients. Fold in egg whites.
Coat waffle iron with nonstick vegetable oil spray. Pour batter onto iron, spreading it into corners (amount of batter needed will vary depending on your machine, we found a 1/4 cup to be about right for each waffle square). Scatter bits of ham and cheese over each waffle. Cook until golden brown and cooked through. Pop the cooked waffles out (we actually used a bamboo skewer to help get into the tight, deep waffle spaces) and transfer to a baking sheet; keep waffles warm in oven between batches. Serve with butter and warm maple syrup.