Mousse. In large shallow bowl, mix yolks with sugar, water, salt and gelatin. Whip constantly over boiling water until thick and lemon colored. Remove from heat. Add strained lemon juice and zest. Cool to room temperature; reserve. Whip egg whites with 1/4 cup sugar to soft peaks. Temper yolk-lemon mixture with large spoonful of whties. Fold in remainder; reserve. Whip cream with 1/3 cup sugar. Fold into reserved lemon mixture. Pour into 10-inch springform pan with shortbread crust. Chill 2-3 hours. Remove from pan. Garnish with lemon twists. Cut into 8 slices. Serve with caramel sauce, if desired. Shortbread Crust. Whip butter with sugar and salt until light and smooth. Add egg, then flour. Whip until fluffy. Spread into 10-inch springform pan. Bake at 300~ for 10 minutes. Cool. Lemon Mousse Cake has real zest--and juice--from fresh lemons. Mousse rests on rich, tender shortbread crust. Bette...NM ----