Sandra, agreed about box cake mix being "okay", but not as good as WASC or scratch--that's why I'm trying to figure out how to troubleshoot and tweak for a light, fluffy, yet still moist vanilla scratch recipe to go with that frosting. Also, because it's good to have a reliable scratch recipe for when the need/mood arises, and you have pantry staples but no box mix--which I haven't bought in years, since I need to work sugar-free, and the vanilla SF box mix has a very chemical taste. Definitely not a preferred flavor!  

And yes, about that frosting--I'm terrified of trying to make it! So many websites say it's easy, yet I look at it and all I can think of is how easy it would be to make a roomful of people sick with improperly heated egg whites. Or at least gross them out with runny, decomposing frosting...LOL

I'm intimidated by SMBC for the same reason, and for the fact that I've never worked with a candy thermometer. And yet....it always looks so gorgeously light and soft, while holding the shapes of flowers and stringwork perfectly....is it possible to make SMBC with a reliable brand of carton egg whites (like Egg Beaters), to avoid the whole possible-food-poisoning issue?

I am going to share my mother's white cake recipe (we use it for coconut cake, just omit the coconut) that I've been baking for close to 60 years.  It is quite delicate and requires a subtle touch to prevent over mixing, which results in a tough crumb.  The frosting is similar to 7-Minute Frosting.

COCONUT FLUFF CAKE

Sift together:  2-1/2 cups all-purpose flour, 4-1/2 teaspoons baking powder, 1-1/2 teaspoon salt, and 1-3/4 cups sugar /  Add: 3/4 cup melted vegetable shortening and 1-1/8 cup milk / Beat for 2 minutes until batter is well blended and glossy / Add:  1 teaspoon almond extract, 1 teaspoon vanilla extract, and 2/3 cup egg whites / Beat for 2 minutes.  Pour into 2 greased and floured 9" round pans.  Bake at 350 degrees F. for 35 to 40 minutes.

NOTES:  I generally bake at 325 degrees F. and start checking for doneness at 30 minutes.  (The above is the original recipe, as written)  I also use at least twice as much of vanilla and almond extracts as specified.

FLUFFY WHITE FROSTING

Combine 3 egg large whites, 1/4 teaspoon cream of tartar, 3/4 cup sugar, 6 tablespoons light corn syrup, and 1/2 teaspoon salt.  Place in the top of a double boiler ovr rapidly boiling water and beat with rotary beater (see how old this recipe is, lol) for 4 to 5 minutes until mixture stands in soft mounds.  Remove from boiling water and cool.  Add 1 teaspoon vanilla (I use vanilla and almond), continue beating until frosting stands in peaks.  Spread on cool layers of cake  and sprinkle with coconut. 

NOTES:  If you don't have a double boiler, you can use your mixer bowl or any bowl that will fit over a pot of boiling water.  This recipe is glossy, fluffy and delicious, but not real stable, certainly too soft for piping.  It makes a beautiful, fluffy cake, but if not kept refrigerated, tends to break down and slide off the cake.  I use it when the cake can be served shortly after removing from the fridge.

Now, that being said, in a pinch I've used a white cake mix and added a couple of teaspoons of almond and vanilla flavoring and it is pretty close in flavor and texture, an exceptable substitute when necessary.

Don't be afraid of killing anyone with egg whites.  When making SMBC, heating the eggs and sugar over hot water is sufficient to kill the bacteria.  By the time all the sugar is completely dissolved (feels smooth when you rub it between your fingers) the eggs will have reached a safe temp, 130 degrees F.  I like it because it is light and fluffy, much like the recipe above, but much more stable because of all the butter.  It is a very forgiving frosting.  The key is to beat the egg whites and sugar until they are very stiff before you start adding the butter.  If they are still too warm and the frosting deflates when the butter is added, stick it in the fridge for a while until it cools off and resume beating until light and fluffy.  

I was reluctant to give it a try for a long time, then felt stupid for waiting so long, lol.