Preheat oven to 350°F (175°C).

Coat two 9-inch round cake pans with cooking spray and line the bottoms with wax paper.

In a bowl, whisk together sifted cake flour, baking soda, and salt.

In a large bowl, beat softened butter with a mixer until light and fluffy.

Gradually add 1 3/4 cups of sugar to the butter, beating until well blended.

Beat in orange rind and vanilla extract.

Add egg whites one at a time, beating well after each addition.

Combine low-fat buttermilk and nonfat milk in a separate bowl.

Alternately add the flour mixture and buttermilk mixture to the butter mixture, beginning and ending with the flour mixture. Mix until just combined.

Pour batter into prepared cake pans and tap gently to remove air bubbles.

Bake for 25 minutes, or until a wooden pick inserted into the center comes out clean.

Cool in pans for 20 minutes on a wire rack before removing from pans.

Cool completely on a wire rack.

Combine fresh orange juice and the remaining 1/4 cup of sugar in a bowl; stir until the sugar dissolves.

Pierce the cake layers liberally with a wooden pick.

Slowly drizzle the orange juice mixture over the cake layers.

Carefully place one cake layer on a serving plate and spread with 1/3 cup of melted orange marmalade.

Top with the remaining cake layer; spread the remaining marmalade on top of the cake.

Fold low-fat sour cream into thawed reduced-calorie whipped topping.

Spread the sour cream mixture over the sides of the cake.

Cover and chill for at least 2 hours before serving.