Preheat oven to 350°.
To prepare cake, coat a 13 x 9-inch baking dish with cooking spray; dust with 1 tablespoon flour.
Place salt and 4 egg whites in a large bowl; beat with a mixer at high speed until soft peaks form. Gradually add 2/3 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Place 1 teaspoon vanilla and eggs in a large bowl; beat until thick and pale (about 3 minutes). Gently fold egg white mixture into egg mixture. Lightly spoon 2/3 cup flour into dry measuring cups; level with a knife. Gently fold flour into egg mixture. Spoon batter into prepared dish. Bake at 350° for 20 minutes or until cake springs back when touched lightly in center. Cool 5 minutes in pan on a wire rack.
To prepare the milk mixture, combine the half-and-half, condensed milk, and evaporated milk. Pierce the entire top of cake with a fork, and pour the milk mixture over the cake.
To prepare meringue, beat 3 egg whites with a mixer at high speed until foamy. Combine 1 cup sugar and 1/3 cup water in a saucepan; bring to a boil. Cook, without stirring, until candy thermometer registers 238°. Pour hot sugar syrup in a thin stream over egg whites, beating at high speed. Stir in rind and 1 teaspoon vanilla. Spread over cake.