Combine egg yolks, 1/4 cup sugar, butter, peel, juice, and dash salt.
Cook and stir till thickened.
Remove from heat; beat 2 minutes.
Beat egg whites to soft peaks.
Gradually add 1/4 cup sugar; beat to stiff peaks.
Fold yolk mixture into egg whites.
Spoon into four individual souffle dishes.
Place in shallow baking pan; pour hot water into pan to depth of 1/2 inch.
Bake in 350° oven 30 to 35 minutes.
If desired, sprinkle with powdered sugar.