Step 1Whip egg whites at high speed until stiff peaks form, 3 to 4 minutes.
Step 2Beat egg yolks in large bowl. Add flour, ricotta, lemon zest, melted butter, salt and sugar. Mix until batter is smooth. Fold in 1/4 egg whites to lighten batter, then fold in remaining whites. Do not over-mix.
Step 3Lightly coat griddle with nonstick cooking spray. Heat over medium-low heat. Ladle 1/2 cup batter onto griddle for each pancake. Cook pancakes until light brown, 4 minutes, then turn and cook 3 minutes more.