In a mixing bowl, combine flour, baking powder, sugar and salt. Beat egg yolks with milk and butter; add all at once to dry mixture. Stir just until completely moistened (will be lumpy). Separately, beat egg whites to stiff peaks, then fold into batter gently, leaving small bits of egg whites visible to add lightness to the waffles. Let rest 5 min. Meanwhile, heat waffle iron. Spoon approx. 1/3 c of batter into iron or as directed by manufacturer (waffle irons vary in size and style); be careful not to overfill. Cook 4-5 min or until waffles are golden and release easily from iron. Serve immediately with Caramelized Apples & Walnuts and mascarpone.
Caramelized Apples & Walnuts
Warm butter over medium heat in nonstick skillet. Add apples, brown sugar, walnuts and cinnamon. Sauté just until apples soften, approx. 2 min. Add syrup and salt and reduce slightly, approx. 1 min more. Serve immediately.