In a large bowl, combine 1/2 cup sugar, flour and salt. Stir in the milk, lemon juice, butter and lemon zest. Beat egg yolks; add to lemon mixture.
In a small bowl, beat egg whites on medium speed until soft peaks form. Gradually add remaining sugar, 2 tablespoons at a time, beating on high until stiff peaks form and sugar is dissolved. Fold into lemon mixture.
Spoon into six greased 8-oz. ramekins or baking dishes. Place in a 13x9-in. baking pan. Add 1 in. of hot water to pan.
Bake, uncovered, at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Serve immediately or chill.