How to Make It
In a large skillet, melt the 2 tablespoons of butter. Add the apples, cinnamon, 2 tablespoons of the sugar, 1/2 teaspoon of the lemon zest and a pinch of salt and cook over moderately high heat, stirring occasionally, until the apples are just tender and golden, about 5 minutes; keep warm.
In a large bowl, whisk the flour and baking powder with 1/2 teaspoon of salt and the remaining 2 tablespoons of sugar. In a medium bowl, whisk the milk with the egg yolks, ricotta and the remaining 3/4 teaspoon of lemon zest. Whisk the mix into the dry ingredients until just incorporated.
In a clean, large stainless steel bowl, beat the egg whites until stiff peaks form; fold them into the batter.
Preheat a griddle and grease it with butter. Scoop 1/4-cup mounds of batter onto the griddle. Cook the pancakes over moderately high heat until bubbles appear on the surface, 1 to 2 minutes. Flip and cook until the pancakes are risen and golden brown on the bottom, about 2 minutes longer. Transfer to plates, spoon the warm apples on top and serve with warm maple syrup.