Preheat oven to 350 degrees F. Lightly coat six 8-ounce individual souffle dishes with cooking spray; place dishes on a baking sheet. Chill dishes.
In a small saucepan stir together granulated sugar, flour, and salt. Whisk in milk and lemon juice until combined. Cook and stir over medium-low heat for 8 to 10 minutes or until thickened and bubbly. Stir in lemon peel. Remove from heat.
In a large bowl beat egg yolks with an electric mixer on medium to high speed for 3 to 5 minutes or until thick and lemon color. Stir milk mixture into yolks to combine.
Thoroughly wash beaters with warm, soapy water. In another large bowl beat egg whites with an electric mixer on medium to high speed until foamy. Add cream of tartar. Beat on high speed until stiff peaks form (tips stand straight).
Gently fold egg whites into milk mixture. Evenly divide batter among the prepared souffle dishes. Bake about 20 minutes or until a knife inserted near the centers comes out clean. If desired, sift powdered sugar over souffles. Serve immediately.