While the beans are cooking, make the compound butter.
Start with one stick of softened, unsalted butter and place into a mixing bowl that gives you enough room to mash in the preserved lemons.
Rinse one preserved lemon off, and shake off as much water as you can. Cut away the flesh. Remove any seeds.
Use a fork to mash the lemon flesh into the butter, or put both the butter and preserved lemon flesh into a food processor to combine that way.
If you want more lemony flavor, cut some of the rind into smaller pieces and mash in, but taste it frequently. Preserved lemons have a stronger flavor than you'd think.
Use a rubber spatula to manipulate the butter-lemon mixture into a log shape, and wrap in plastic wrap. Add whatever you're going to use to your lima beans right away, and wrap the rest tightly and refrigerate.