Lavender chocolate whoopees

Although this recipe, and the original name, sponge drops, derive from the 1950s English baking repertoire, they were made in the same way as whoopee pies, which have recently had a brief revival and, like them, were probably a way of using up left-over cake batter; the whoopee pie is said to have originated in the thrifty Amish kitchens of Pennsylvania.