Beat egg yolks at medium speed of an electric mixer until thick and lemon colored.
Sprinkle gelatin over cold water in a saucepan; let stand 1 minute.
Cook over low heat, stirring until gelatin dissolves, about 2 minutes.
Stir in yolks,1/2 cup sugar, and salt.
Cook over medium heat, stirring constantly, until mixture begins to boil.
Remove from heat; stir in lemon rind and juice.
Cool.
Combine egg whites and remaining 1/2 cup sugar in top of a double boiler.
Place over simmering water.
Cook, stirring constantly with a wire whisk, 7 minutes or until mixture reaches 160°.
Remove from heat.
Beat at high speed 3 minutes or until soft peaks form.
Fold egg white mixture and whipped cream into yolk mixture.
Spoon into a 1 1/2 quart dish; cover and chill.