Orange Sponge Cake
["1 1/3 c. flour", "1 Tbsp. grated orange peel", "6 eggs, separated", "1 tsp. cream of tartar", "1 1/2 c. sugar", "1/2 c. orange juice", "1/4 tsp. salt"]
["Combine flour and 1/3 cup sugar; set aside.", "Beat egg yolks until thick and lemon colored (about 3 to 5 minutes).", "Add orange peel and juice; beat until very thick.", "Gradually add 2/3 cup sugar and salt, beating constantly.", "Sift flour mixture over egg yolk mixture a little at a time, folding just until blended.", "Wash beaters.", "Beat egg whites with cream of tartar until soft peaks form.", "Gradually add 1/2 cup sugar, beating until stiff peaks form.", "Thoroughly fold yolk mixture into whites.", "Bake in ungreased 10-inch tube pan at 325\u00b0 for about 55 minutes.", "Invert cake in pan to cool."]
["flour", "eggs", "cream of tartar", "sugar", "orange juice", "salt"]