1 1/2 c. sifted cake flour
3/4 c. sugar
1 1/2 tsp. baking powder
1/2 tsp. salt
1/4 c. water
1/4 c. vegetable oil
3 eggs, separated
3 tbsp. grapefruit juice
1/2 tsp. grated lemon rind
1/4 tsp. cream of tartar

Sift together flour, sugar, baking powder and salt into mixing bowl. Make a well in center of dry ingredients. Add water, oil, egg yolks, grapefruit juice and lemon rind. Beat until smooth. Beat egg whites and cream of tartar separately until whites are stiff but not dry. Gradually pour egg yolk mixture over whites, folding gently with a rubber spatula until just blended. DO NOT STIR mixture. Pour into greased pan. Bake at 350 degrees for 25 to 30 minutes, or until cake springs back when lightly touched with finger. Invert pan on cake rack until cool. Run spatula around edge of cake. Carefully remove from pan. With a serrated knife, gently cut layer in half. Finish with Grapefruit Cream Cheese Frosting (recipe follows).