Preheat oven to 350°F. In a large bowl combine egg whites and cream of tartar. Beat with an electric mixer on medium-high speed for 1 to 2 minutes or until frothy. Reduce speed to medium; gradually add ½ cup sugar. Increase speed to medium-high; beat egg whites until soft peaks form (tips curl). Add poppy seeds, the 1 teaspoon lemon peel, the lemon juice, vanilla, and food coloring. Beat for 2 minutes more.
In a separate bowl sift together cake flour and ½ cup sugar. Using a rubber spatula, gently fold one-fourth of the flour mixture into the egg whites. Repeat, folding in the remaining flour mixture one-fourth at a time.
Pour cake batter into an ungreased 10-inch tube pan. Bake for 30 to 35 minutes or until cake top is lightly golden and springs back when lightly touched. Immediately invert cake in pan; cool completely.
While cake is cooling, prepare Lemon Glaze: In a small bowl combine powdered sugar, lemon peel, and lemon juice. Whisk until smooth.
Loosen sides of cake from pan; remove cake from pan. Just before serving, pour Lemon Glaze over cake. If desired, serve with dollops of dessert topping sprinkled with additional finely shredded lemon peel.
Tip: We do not recommend sugar substitutes for this recipe.