This is a splurge-worthy cake, wonderful for spring and summer. I've given some other suggestions below for giving the cake a more "enlightened" profile. I have made the cake with all of these variations with great success.
I wouldn't recommend making additional changes; if you start to vary quantities (i.e., of sugar, flour, fat), the cake will be greatly compromised. As in, "Wow, this tastes just like a lemon brick!" For example, I call for half butter (for flavor), half shortening (for airiness and height) in the cake layers; if you use all butter, the layers will not rise as high.
I get annoyed when people go to far with the "baking is a a science, you can never make changes!" That's a silly overstatement; we would never have baking innovations if that were the case. Nevertheless, changes must be made with caution and care and may require several rounds of trial and error before having that "Eureka!" moment.
So save the cake for an occasion where you are ready to splurge and enjoy every delicious bite!
Sunny Lemon Cake
From Piece of Cake! by Camilla V. Saulsbury © 2011 Robert Rose Inc. www.robertrose.ca Reprinted with permission. All rights reserved.
Bright and tangy, this is my idea of the perfect layer cake. You may think its tart-sweet flavor is for adults, but you'll be surprised: children adore it too. Although good all year, it seems to be the perfect dessert to celebrate the start of summer (some first-of-the-season berries make a gorgeous crown).
In a large bowl, whisk together flour, sugar, baking powder and salt.
Add eggs, buttermilk, butter, shortening, lemon zest and lemon juice to flour mixture. Using an electric mixer on medium-low speed, beat for 1 minute, until blended. Scrape sides and bottom of bowl with a spatula. Beat on high speed for 2 minutes. Add lemon-lime soda and vanilla; beat on low speed for 15 to 30 seconds, until just blended.
Spread batter evenly in prepared pans, dividing equally.
Bake in preheated oven for 25 to 30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs attached. Let cool in pans on a wire rack for 10 minutes. Run a knife around edge of pans, then invert cakes onto rack to cool completely.
Place one cake layer, flat side up, on a cake plate or platter. Spread 3⁄4 cup of the frosting evenly over bottom layer. Top with the second cake layer, flat side down. Spread the remaining frosting over top and sides of cake. Refrigerate for 1 hour before serving.
Butter Note: This is a one-bowl cake, which means the butter and sugar are not creamed separately from the remaining ingredients--they are all combined in one fell swoop. That means it is extra-important to make sure your butter is really softened; otherwise, the butter will not be completely incorporated into the butter.
How soft? You should be able to drag your finger through the butter with ease (yet it should not be melting). To speed up the process, grate the butter using the large holes of a cheese grater. Even rock hard butter will be soft in about 5 minutes!