Whip the egg whites: In a clean, dry bowl, whisk the egg whites to soft peaks, then continue until they are firm and hold their shape.
Make the batter: In a separate large bowl, mix the egg yolks, salt, and sugar until well blended. Mix in the melted butter, flour, baking powder, ricotta cheese, and lemon zest until smooth.
Fold: Gently fold the whipped egg whites into the batter until just combined — do not over-mix.
Prep the pan: Spray an air-fryer-safe cake pan (about 7 inches) with non-stick cooking spray and pour in the batter.
Air fry: Bake at 320 degrees F, air fryer setting, for 20 minutes. Insert a toothpick in the center — if it doesn't come out clean, air fry another 5 minutes and check again.
Cool and serve: Cool in the pan 10 minutes, turn out, dust with powdered sugar, slice, and enjoy!