Orange Cake with Orange Frosting

3 c. Sugar
1c. Butter, softened, unsalted
6 egg whites
1 Tablespoon vanilla
Zest of  1 orange
2c. Buttermilk
1 tsp. baking soda
1/2 tsp. baking powder
3/4 teaspoon salt
4 c. Cake flour

Cream butter, sugar. Add vanilla, rind. Add 1 cup buttermilk,  baking powderand soda, salt. Add 2 cups cake flour. Add the rest of the buttermilk and flour. Whip egg whites. Gentily fold in egg whites. Prepare three 9" round cake pans by buttering and lining with parchment or wax paper. Bake 350 for 20 minutes. Reduce heat to 325 and bake 25 minutes. Let COOL. 

Frosting
3 cups powdered sugar
1/3 cup softened butter
1 teaspoon vanilla
Juice of about 1/2 orange
Cool whip or a little whipping cream

Mix all except the juice. Slowly add the juice. Do not make it too thin, you can add more powdered sugar and butter, if it becomes too thin. Frost and serve.