To lighten traditionally dense pound cake, we separated the eggs, a trick we learned from Kathryn King of Atlanta’s Aria restaurant. Beating the whites resulted in a texture reminiscent of angel food cake, while the yolks and butter preserved the rich pound cake flavor. Baking soda made the cake even lighter, and a combination of lemon zest and juice produced a more complex citrus flavor. Begin checking the cake for doneness after 40 minutes and check frequently thereafter. At Aria, slices of the cake are buttered, toasted and served with fresh fruit and whipped cream.