The baseline

The 1950s were the era of free promotional recipe booklets, and 7UP’s advertising campaign at the time touted soda-as-ingredient recipes like 7UP Salad (blend lime Jell-O, applesauce, and soda) and 7UP Parfait Pie (add the soda to both ice cream filling and crust). Over the years, most of these recipes have (mercifully) been forgotten, but 7UP Pound Cake remains a treasured favorite. While traditional pound cakes can be dense, the 7UP version has a tight yet light crumb, thanks to the soda’s citric acid (which tenderizes) and carbonated water (which lifts).

Element of distress

Unfortunately, the flavor didn’t wow us as much as the texture. The 7UP cake recipe made with soda plus lemon extract tasted like it was dusted with furniture polish, while the sugar (a generous 3 cups) overwhelmed the citrus flavor of 7UP cake recipes augmented with lemon zest. Also, every last recipe omitted lime juice, extract, or zest altogether—surprising, given 7UP’s hallmark lemon-lime combination.

Line of attack

We’d scale back the sugar and achieve the perfect punch of citrus for a cake with a taste as uplifting as its texture.

Onward

We set out to perfect the fine balance of sweetness and citrus tang. Cutting out ½ cup of sugar certainly helped, but the flavor of the cake remained flat. Unlike juice, finely grated zest can be added without affecting texture, so we added increasing amounts of both lemon and lime zest until we topped off at 1 tablespoon of each. The zest lent a fragrant quality, but the cake still lacked conviction, so we tossed lime and lemon juices into the mix.

Now the cake tasted great, but the texture had taken a turn for the worse. A perfect pound cake hinges on a fragile emulsion of butter and eggs; the extra acid (from the juice) was causing the batter to curdle, resulting in a tough, gummy cake.

So close, but not enough. How to put the uplifting texture back in our 7UP cake? The test kitchen has had success using melted butter in acidic cake batters. We simply melted the butter and, using a technique the test kitchen has liked in the past, pulled out the food processor. (The brawn of the machine ensures the emulsification.) Once the sugar and wet ingredients were combined, the melted butter is slowly poured down the feed tube.

That did the trick: The cake emerged with a fine, even crumb plus a forceful lemon-lime flavor. When life hands you lemon-limes, you make lemon-lime soda cake.