Prepare Lemon Sauce; set aside.
Preheat oven to 350°.
Lightly spoon flour into a dry measuring cup; level with a knife. Sift together flour and next 3 ingredients.
Beat egg whites until foamy. Add cream of tartar; beat until soft peaks form. Add sugar, 2 tablespoons at a time, beating until stiff peaks form. Slowly pour in molasses, beating egg white mixture until sugar dissolves. Fold in flour mixture over egg white mixture, 1/4 cup at a time. Add vanilla.
Spoon batter into an ungreased 10-inch tube pan, spreading evenly. Break air pockets by cutting through batter with a knife. Bake at 350° for 35 to 38 minutes or until cake springs back when lightly touched. Invert cake pan; cool completely. Loosen cake from sides of pan, using a narrow metal spatula. Invert cake onto plate. Serve with Lemon Sauce.