Heat a nonstick griddle to medium-high heat.
Mix together the flour, sugar, salt, lemon zest, ricotta, and yolks in a large bowl until thoroughly combined.
Beat the egg whites in a separate bowl until stiff. Fold the egg whites into the ricotta mixture.
Spread some butter on the hot pancake griddle.
Ladle 1/2-cup size pancakes onto the hot griddle and cook for about 2 minutes per side, until golden. Keep pancakes warm in a 200 degree F oven before serving.
Serves: 4 (analysis done with part-skim ricotta and 2 tablespoons of unsalted butter); Calories: 320; Total Fat: 18 grams; Saturated Fat: 10 grams; Protein: 19 grams; Total carbohydrates:20 grams; Sugar: 4 grams; Fiber: 0.5 gram; Cholesterol: 256 milligrams; Sodium: 247 milligrams