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 low oven before serving.