In a mixing bowl, combine flour, sugar, baking powder, cinnamon, and salt. In another bowl, beat egg yolks slightly. Beat in milk and cooking oil. Add the egg-yolk mixture to the flour mixture all at once. Stir just until combined, but still slightly lumpy. Stir in the chopped apple.
In a small bowl, beat egg whites until stiff peaks form (peaks stand straight). Gently fold beaten egg whites into batter, leaving a few fluffs of egg white. Do not over mix.
Pour some of the batter onto grids of a preheated, lightly greased waffle baker. Close lid quickly; don't open during baking. Bake according to manufacturer's directions. When done, use a fork to lift waffle off grid. Repeat with remaining batter.
Serve with warm maple syrup and butter. Top with fresh fruit, if you like. Makes about 4 waffles.