In a large bowl, combine the first seven ingredients. Sift together the flour, sugar, baking powder and salt; gradually beat into lemon mixture until smooth. In a small bowl, beat egg whites until foamy. Add cream of tartar; beat until stiff peaks form. Gently fold into the lemon mixture.
Pour into an ungreased 10-in. tube pan. Bake at 325° for 45-55 minutes or until cake springs back when lightly touched. Immediately invert pan; cool completely. Remove cake to a serving platter. Combine glaze ingredients; drizzle over cake.