These custards are inspired by the Japanese egg custard chawan mushi, made with dashi broth (a stock of dried kelp and dried bonito flakes). We've used chicken broth for simplicity, but any broth or stock that you have on hand will work fine.
Steaming the custards gives them a delicate texture, which is enhanced by the spare use of solid ingredients (the shrimp, scallion, and mushrooms).