1 Preheat oven to 350 degrees F (175 degrees C). Grease and flour an 8 inch square pan.
2 In a large bowl, combine sugar, salt and melted butter. Beat in the flour. Stir in the lemon zest and lemon juice. Combine milk and egg yolks, and add to lemon mixture.
3 In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into the batter, then quickly fold in remaining whites until no streaks remain. Pour batter into prepared pan.
4 Set cake pan in a water bath. Bake in the preheated oven for 40 minutes, or until top is lightly browned. Serve warm or cold.